Regained? As in you know for a fact you have zero sperm count??
I've seen plenty of guys go on Clomid therapy after years of HRT or cycling and get wives/gf pregnant.
Also it is a myth you can't get pregnant on cycle or HRT. I have seen hundreds of men get wives/gf pregnant while on cycle, while on HRT. My first daughter, I was on cycle, my last one, I was on prescription HRT.
Alot of it is individual.
If you need to improve sperm count, look into Clomid use, HCG and HMG. Several months of therapy can be very successful for many.