Your assumptions about panic=abort are correct, it will simply terminate the entire process. The single thread and multithreaded behaviors are technically the same. A thread can observe the panic of another, as such, in a single threaded app, which thread would observe the panic in the main thread? There is no other thread to do that.

What you could do is create a single new thread and pretend as though its the main thread, observing any panics on the original main thread.

Edit: your mental model should be to avoid thinking about panics (beyond avoiding them in the first place). Panics are supposed to be extremely rare, and typically something that would be difficult to recover from. They are not exceptions; they are not designed to be caught. The difficulty in dealing with them is a feature that prevents anti patterns. If something panics you have a bug.