This happened to me, thrice already. I bought it from this thrift online website called Carousel.
The first time it happens, I think I almost $@$* my pants. But now that it happened thrice - here's my intake for it;
# No nothing will &&^&^$^ happen even when you change the battery. You can try your luck but I think 9/10 it won't work
# You won't get to safe ANY your current film cartridge. It happens again and again to me. I didn't get to safe any of it. But if you still want your camera and don't mind about buying new film cartridge; this is what I do
# Open the back and cut open the cartridge film be careful to not damage the upper part as the stuck film is still holding it tight and it might damage the projector (I just use normal scissors for this. JUST be careful pls)
# Once you've cut it open take all of the unused film out and you'll find the stuck film at the very back of the cartridge. Pull it by swigglin and do zigzaggin motion on it slowly
# Another thing I realized is DO NOT PUT ON YOUR CARTRIDGE OF FILM when the BATTERY HAS ALREADY BEEN INSERTED. For some reason it jacked off the projector. Always put the cartridge of film first. Then your batteries
I guess that's it. This might not be the most sophisticated way. Truth be told its a lambo way to get $@$* done. But I still can use my Mini 8 after 3 years I bought it. God knows how many years has the previous owner used it. Aite that's it. Hope it helps. Or not lmao ciaoooo