Me too! After six years of skimo racing, I’m starting to do some climbing again.
What I’ve found is that rock climbing training is very low volume, so maintaining some aerobic fitness is definitely possible. My aerobic volume is about 75% of what it was, and I haven’t notice any drop off in aerobic threshold speed. However, the duration that I can maintain that speed has fallen.
I periodize it by having high-load climbing workouts first thing after a rest day. More moderate-load workouts don’t need as much recovery beforehand.
Does that help?