Generally riding a bike until its unrideable is a good way to permanently ruin whatever parts could have been repaired. Most folks would tell you to stop and repair the bike before it get to the point where its unrideable.

Things that typically need repair/service are the Headset, the BB, the Hubs and the drivetrain. For the most part on vintage bikes these parts all have loose ball bearings inside them that periodically need to be re-greased and at some point in the bike's life will need to be replaced with new ones. Its just normal wear and tear. Other parts don't typically get serviced/repaired but simply thrown out and replaced. Like Brake and Shifter Cables, Brake Pads, Cassettes and Chainrings.

If you can post some pictures it will help determine how far gone it is and what should be done to bring it back into service.