If chain/ BB/ casette are dead can chainrings and derailleurs still be OK?
The load is spread across more teeth on the chainrings than on the cassette, so they tend to last quite a bit longer.  If they said your chainrings are fine, then they are probably no problem.  derailleurs don't really have many parts that can wear out. There isn't much load being placed on the jockey wheels, so they can last quite a long time. The spring which returns the derailleur when shifting should also last very long. There's no reason to assume that the wear on the cassette, chain, and bottom bracket, would mean that the chainrings and derailleurs are about to die.

That being said, if you are planning on doing another long cross country tour, you might want to replace them ahead of time. I wouldn't want to be stuck in the middle of Saskatchewan trying to get replacement parts.  If you're just going to be doing short trips there's no reason to replace these parts prematurely.