I've built a front wheel with alloy nipples, and eventually had the nipple heads break off of the body of the nipple. I've since learned that the spoke should extend through the whole nipple to reduce the chance of this. That wheel got brass nipples once a couple of alloy nipples broke.

I currently have a different front wheel with alloy nipples, and it's got a lot(?) of miles. Probably 10k or more? fwiw, the wheel has 36 spokes. No problems so far.

I never had the nerve to try alloy nipples on the rear wheel though. (and I'm not a heavy person) If your broken nipple was on the drive side, I'd probably start with just replacing that side with brass nipples. They get more tension and are more highly stressed.
A more pragmatic person might just decide to replace all of the alloy nipples as long as the wheel is getting re-tensioned and re-trued... but where's the adventure of that??

Steve in Peoria