How many times would you use a set of head bolts? Would it strictly be based on # times torqued down? Can you factor how little run time on the engine before removing the heads?

I would use them as many times as you want. That last question I don't understand.

Since the OP doesn;t mention what engine, or what brand headbolts, the answer is, it depends.

If they are tor to yield then you not supposed to reuse them. Though I have.

If they are out old school style head bolts, or aftermarket stuff like ARP, then they are reuseable indefinitely as long as you don't over stretch them.

426, ARPs... Thanks!

I think your grandkids can use them.

From ARP:

Are ARP bolts and studs re-usable?

Yes. As long as the fasteners have been installed and torqued correctly, and show no visible signs of damage, they can be re-used. If they show any signs of thread galling or corrosion, they should be replaced. In the case of rod bolts, if any of them have taken a permanent set and have stretched by .001” or longer, you should replace them immediately. See page 29 in the catalog for more detailed information on this critical measurement.