Maybe retire it from Cyclocross and use it for commuting only, assuming your commute is less demanding than your cross riding.
I don't have a hard and fast rule for replacement. I have never had a rim fail, which says to me that I replace on the conservative side and I have not had a defective rim. If I had to guess, I replace the rim when the sidewall is about 25% worn through. I would ride them on road bikes but I usually don't have any 26" road bikes.