So I take fairly good care of my chain, rings, and cassette. Today I noticed a little bit of rust on 2-3 links. Does this mean it is the end of my chain?

I've had the bike for a year. The bike is a pass down from 3 generations ('91 Klein Quantum) I do NOT know the last time the chain was replaced, yes it is stretched, yes the entire drivetrain has worn down with the chain, no I do not have enough money to replace the entire drivetrain.

Again,
1. Is this the end for the chain?
2. Is there anything I can do to keep using it?
3. Will a new chain on very old rings and cassette make shifting catastrophic?