I had a bugged expedition too. A way to fix is was building a new building over the bugged chopper, and deleting it. It frees the staff, and you can replace the chopper.

I have experienced the same bug and so far have been unable to solve it. Building over the helipad seems blocked.

Hello,

So Sorry about this! 

We're investigating the problem and hope to fix it ASAP.

If you're able to upload your TPM folder (located here C:\Users\<username>\AppData\LocalLow\Two Point Studios\Two Point Museum) to this bug, we'd really appreciate it. 

Thanks for your patience, 

Chizel

Same bug described above. Also noted a janior seems to be stuck underground. Unable to fire the staff, unable to sell the helipad, and unable to explore the 'locked' location with a second helicopter. Restart did not help and check file integrity did not alleviate. Please help!

Helicopter is stuck as two employees both janitors are unable to board the helicopter. Making the helicopter unable to take off and bugging it out. Tried building over it and it didn't work. Tried reloading didn't work, tried uninstalling and reinstalling, didn't work. Pear SHaped 1 star objective is now impossible to complete as whirlcog supplies is locked behind one POI on the maps and cannot be accessed by an bother helicopter once one is set to go on a mission. 

after my staff was stuck in the hopper i deleted it throught demolition, and now my staff is fully unresponsive, cant fire, move them or anything, sending them on another expedition is possible, thought it did not do anything, for me it was in space museum

I have the same bug, in 2.0. Like said before, the workaround of building ontop of the helipad doesn't fix it, just comes up with an "items blocked" message.