Ok, now we have a real touch of fall in my area. Warm days and getting colder nights.

Can frost be far behind?

Can I expect some die back on my sempervivums? Should I repot any now?

No, frost does not kill them, they love winter weather. Just not cold/dry wind, which will suck the moisture out of them.
If they are growing well I would leave them along until spring for repotting.

Normally I don't have a lot of winter die-back, but it's not uncommon to lose a few, especially if they don't have a good root system yet.