What glue should I use to fix this?
Will it even hold considering the size of the crack?
I can't replace the shell now since I need the drone for recording atm
I've used super glue and it worked perfectly. I dabbed a LITTLE bit on the crack and a tiny amount seeped in the crack itself and gave it a great seal. The crack has not grown and it is holding up nicely. I must mention though that the crack on mine was much smaller than the one in your pic
I would recommend you to send it for check and repair as glue may void your warranty. Please create the repair case from here: https://repair.dji.com/en/SelfRepair/Area