Hi,I defeated the chopper using the rocket launcher and the first time it crashed and created an hole as it should be,then i had to quit the game and when I loaded my save i bumped into this bug: the chopper crashes but then disappear and there is no hole,however if I walk on the part of the floor where the hole should be I receive fire damage like it should be if there was the burning chopper.Thank you in advance for help

I had a different glitch there where I could not get out of the building after the chopper crashed (I fell through the hole it created when it crashed).
I ended up having to restart the level.

Not sure this is a bug coz I saw 2 versions here

If there is a hole in the floor finding the exit is a bit of search down there.
If there is no hole in the floor the exit door on your floor is open (after you killed every opponent) and you can go that way.

Looks to me you can have multiple exit scenarios actually a nice touch!