Scooby,
Way back my oncologist spoke of "rechallenging" the PCa with repeated docetaxel. This was after abiraterone and cabazitaxel, so repeated docetaxel is a recognised way ahead. Also lots of our contributors here have had more than the standard six cycles, as I and no doubt your husband had. For good reason, I didn't take that route but I wouldn't hesitate in the future as I found that chemo to be easy to handle (relative to other chemo regimes, that is).
AC