They won't put you in a hospital for the rest of your life. No insurance would cover that.
Major depression comes with the feeling that it's here forever. I used to think exactly the same as you -- that I will kill myself, that it's just a question of "when", that nobody can help me. Guess what -- I was wrong. But I would never have found out if I indeed killed myself. I don't want to say "suicide is a permanent solution to a temporary problem" because maybe your problem is temporary and maybe it isn't. But suicide *is* forever. You don't get a second chance to try and see if perhaps there was another option.
I have no idea if your thyroid illness can be related to how you are feeling emotionally. I know that thyroid malfunction can mimic bipolar disorder symptoms though, so I wouldn't be entirely surprised. I hope your surgery goes well on the 29th, and if not, that you will give psychiatrists at least a chance or two. I mean, the final option is always there, even if you wait a while. So why not try
all other options first? One of them might just work. (This is exactly what I forgot when I was attempting suicide myself -- to try other options FIRST.)
There is an interesting book -- I recommended it to someone else this week but I swear I didn't write it

"How I Stayed Alive When My Brain Was Trying To Kill Me" by Susan Blauner. It helped me stay alive so far. Might be going back to it at some point.
Big hugs -- I hope you stay safe and that your surgery goes well.
Currently working on my upcoming signature.