Good day everybody.
I went out flying with my mini 2 today, after taking a few awesome shot I've packed up my mini 2 and went home. When I got home, I took out the mini 2 from the hard case to remove the battery and saw the drone was never switch off. From where I went flying to my home is approximately 5 min. Can this harm the drone or something on the circuit board?
(Attached is a photo of my hard case)

Kind regards,
Nico

Prolonged I would say maybe, why? because the drone does get warm if sat in the open-air powered-on but without the motors running. Inside the case it is surrounded by insulation which will trap heat.
I do not know if DJI have included a high temperature shut down in the software but I sort of hope so.
If the drone still works I would say got away with it but it might be an good idea to ensure the drone is off before you put it in the case AND to check that nothing could switch it on in the case.
It looks like you have the storage space to remove the battery and store in a recess, that would ensure there was no chance of an accidental switch on.

Unless it has overheated it should be Ok. Just fire it up and check if everything seems ok . It most likely is.

So far everything seems okay, a bit dumb from my side. I'm a control freak, so I always double-check everything............

Maybe a dumb question... But if overheated, will I get a message or notification on the app?

Always remove batteries and place them back in their carrier when done.  If you make -that- a habit, this issue will never happen again.
I have gotten overheat warnings before while playing with settings, drone on, no motors turning.  As well I have got warnings when flying in the winter, for too cold.

Nienco Posted at 3-26 09:47
Maybe a dumb question... But if overheated, will I get a message or notification on the app?

You will get a message on the Fly App if it overheats.  

A few minutes, as you indicate, shouldn't make too much risk of harm. Chances are you didn't perform the switch-off sequence properly.  I always remove the battery from the drone after a flight, to allow it to cool down.  Transporting the drone with the battery in is maybe best avoided.

Just a point and just covering all the bases, in circumstances such as this 'accident', I doubt there would be a warning. For the simple reason that is is unlikely that phone was connected to the controller/drone.

Hello there Nico. Thank you for reaching out and for sharing these information with us. If your DJI Mini 2 overheated you will be receiving an error message on the DJI Fly application and this might affect your DJI Mini 2 as well. Thank you.

When I took the drone out of the hard case, it was hot (not a hot when getting an update). I've checked everything and everything still seemed fine (no burning smell in the drone).

When I connected my phone to the controller and drone, there was no message (but then again, it's not 100% clear if I will get a message if my phone was not connected to the controller and drone). I took the drone for a flight and everything still seems okay (hope I won't get any surprises in the long run).

Normally I take the battery out after a flight, then the one time I don't I almost got myself in an expensive situation.

Thank you for all the advice!

@Nienco
I hope you don't me asking which case is it that you are using? I ask because I searched Amazon for hard cases and could only find one that allowed the Mini 2 to be stored with it's wings expanded.  However the reviews for the product put me off, as they mentioned that the blades swing loose in the box.

@neoborg

The case I'm using is the TOMcase - ready-to-fly.

https://www.dronedepot.be/product/ready-to-fly-case-dji-mini-2/

The arms fall deeper into the case and prevent the blades to swing loose, they also have it in a backpack.
The cases are made by a Germen company - https://tomcase.de/

Nienco Posted at 3-27 01:15
(but then again, it's not 100% clear if I will get a message if my phone was not connected to the controller and drone). I took the drone for a flight and everything still seems okay (hope I won't get any surprises in the long run).

Nienco, if you think "but then again, it's not 100% clear if I will get a message if my phone was not connected to the controller and drone). " perhaps you could explain the method of communication between the drone and the phone when the phone is not connected to the controller.

I would suggest an experiment.
Connect everything and switch everything on as if you were going to fly the drone.
When all is ready you see an image, on the phone's screen, of what the drone's camera sees, is that correct?  
Touch the phone's screen and, keeping your finger in contact with the screen, move your finger slowly up and down the screen, does the gimbal follow the 'vertical' movement of your finger on the screen? If yes both the image and the movement of the gimbal demonstrate that the phone is communicating with the drone via the controller, do you agree?
Doing nothing else unplug the cable from the phone, what happens? You lose the live image on the phone's screen and what image there is goes to black and white. correct? Is th? Try the moving your finger up and down the screen experiment again, what happens to the gimbal? Nothing?
There is no communication between the drone and the phone. How could the drone let the phone know that the drone is getting hot?
If you like try to start the ''find my drone'' function and press ''START FLASHING AND BEEPING'', if anything happens take note of any messages that pop up.
With the early Fly App (pre  1.2 ) that I use for my Mavic Mini I get a message saying "Aircraft not connected. Unable to start flashing and beeping."  With the 1.3 App I use for my mini 2 there is no message, nothing happens.

With the appropriate phone disconnected from the appropriate controller neither of my drones starts beeping or flashing when trying this.

@Sean-bumble-bee

I work in the building laser industry, where you can connect your phone to the laser to adjust settings (rotation speed, slope etc.). Most of the lasers have a shock sensor and a memory chip build into the laser. When your phone is not connected (or no communication between the laser and the phone) to the laser and the laser gets dropped, you get an indication or message that the laser was dropped when you connect the phone to the laser.

So this is possible in a building laser which is not as advanced as a drone, I would have thought that this would also be possible in the mini 2 or any other drone.

Having some kind of memory chip in the drone to keep track of everything (when not connected to the phone) does not sound that farfetched or in my opinion not a bad idea.

Ahhhh you are, I think, talking about  "after the fact" communication, If I am correct then fair enough but, as far as I know, that does not happen between the phone and the Mini 2.
However there is a DAT recorded on the drone, switch on to switch off, in which "drone temperature" is probably recorded BUT that DAT is not transmitted to the phone and is accessed via the appropriate Assistant 2 software on a computer and a USB cable connection to the drone. BUT that DAT is encrypted and unreadable by us mere mortals, As is, I think, the DAT on the drone's mSD card. Only DJI can read the DAT off the drone, this is a blooming shame as it would be quite useful.
My Phantom 3's record a readable DAT on the drone but' Mavics' do not.

Nienco Posted at 3-26 09:47
Maybe a dumb question... But if overheated, will I get a message or notification on the app?

I had that on the MP once (overheat message)