What I would do in this stripped-thread situation, to squeeze more
use out of the bike, is this: I'd clean all the grease out of the
bottom bracket and finish with an alcohol scrubbing. Then, I'd apply
some metal-mending epoxy putty (JB-Weld is good) to the threads, before
installing the inner parts. This would cause a permanent lock, so you
couldn't adjust the bearing cups or add grease later. I'd use the
standard putty, not the quick-set type, so I could properly set the
adjustable cup, before it hardened.
If only the right-side fixed cup is stripped, I'd use putty on it only
and the left-side cup could still be adjusted. Grease would need to be
added to the bearing cups, but kept out of their epoxied threads during
insertion.

This is a last-resort solution, but I've salvaged a longer
working-life out of many different things that had stripped threads, by
using it. I've even fixed broken frame tubes out on the road, by using
several wraps of fiberglass reinforcing cloth and epoxy resin, from my
extensive repair kit. Sometimes I've inserted part of a metal tire-iron
under the cloth, to make a splint. This might also be done using duct
tape, in a more urgent and temporary solution.

Steve McDonald