No matter how long he can maintain a boner for, there's only so much sperm he can produce at once. At some point, he'd just be shooting blanks.
I was going to suggest they should "harvest" his semen but then I realized fertilization doesn't work for reasons... ugh. Perhaps a specific diet could help a little, I've heard certain foods can increase semen production.
@boag fucking incel lol do you have any idea how fucked society would be without the other sex? Get your fucking ass ready, because there'd be be so much homosexual rape if all women died out. You might even finally get some action yourself.