There is nothing on a 777 called a comms mast. There are vhf antennas, hf antennas, tcas antenna, satcom antenna, no comms mast though. These antenna are attached with fasteners, not adhesive. If one did depart the aircraft the “hole” uncovered would not be a pressurization challenge for the two massive engines to compensate for.
I am sure you are correct on this, I did not look up all the antennae on the trip seven. Apparently there are a lot, and they are not mounted on a mast, like a boat.
However, there is a problem with the antenna mounting. I just googled 'Boeing 777 antennas problems' and guess what I found! So please forgive me for not using the exact terminology. Now tell what would happen if the structural part holding the antenna failed and fell off? Would it make a hole big enough to overcome the engines compression limit? I am sure there are alarms and such, but just suppose this did happen, the crew put on their oxygen masks, and the bottles were empty. In other words, and accident chain happened. Ta-Da! Now the pilots are incapacitated. So what is wrong with my idea? It is simple, Tell me what would keep this from happening?
It is easy to remark the words are wrong. I made this simple for a reason. Let's not get hung up on terminology.