You could go for a track chain/chainrings that would be wider/theoretically stronger. But I think you are really chasing something that doesn't matter much. You got a used bike that was somewhat out of adjustment/worn and you didn't correct for this. If you just keep the eccentric adjusted properly, you are very unlikely to have further problems.
The real question is how to make your stoker feel comfortable again. I'd probably replace the chainrings regardless of their wear just to make the stoker feel better that you replaced everything with new parts. Or you might look into a belt drive for the timing chain, this could address your stoker's worry.