I am a novice mini 2 flyer.  I always fly visual line if sight and usually less that 100 feet.

In the Preflight Check page I have the Max Altitude at 390 feet and the Max Distance at 1500 feet.

My question is, if I try to fly beyond those preset values what will happen?  Do I get  a warning and the drone continues or does that drone stop at that wall and hover?  Or does something else happen?

You will get a warning message that you have reached the Max Altitude/Distance and the drone will stop and hover.  You can test this for yourself by setting lower limits within your VLOS and see exactly what happens.  The settings are under the Safety Tab (click on the 3 dots, then Safety Tab, from the camera view screen in DJI Fly).

Try setting lesser distances and test to see what happens.

Hello there Ontario Drone. Good day and thank you for these information that you have given. Once you have fly beyond those preset values you will receive a notification on the DJI Fly application as posted above by K9JDN on post #2. Thank you and fly safe always.

Its like flying into an invisible wall.

Drone will stop and hover.  I'd recommend lowering your max distance and give it a test.  That way you will see how it acts.  

I did a test.  I set the max distance at 49 feet then flew away at speed.   At 49 feet two things happened at the same time., the drone stopped dead then hovered and the controller hummed and vibrated very briefly.  Thanks everyone.