Rust. Lol. Listen,when I went to rehab my girlfriend's old crappy mountain bike which had been sitting in the rain for years just under a tarp, the chain was rusted to ****. All I did was dump a bunch of chain lube on it and work it a bit and it loosened right up. Looks ugly as heck, but works just fine. Not ideal, perhaps, but given how seldom she rides it, it wasn't really worth the effort of a new chain.

So, no, rust is not the end of a chain.