Yes many couples still have sex often then. But many couples don’t anymore.
True. But that's irrelevant if one of the partners is still very much wanting it.
Yes he could separate but what are his chances to find someone he loves, that he is truly happy with (which sounds like is the case with the DW) AND can have sex with? I mean I’m pretty sure he’ll find sex if he wants to, but the rest?
I don't know actually. I saw a video some years ago on YT by a relationship expert who said the chances of finding true love increase as you get older as opposed to younger. Much more so after 40. I imagine 40/50/60 year olds have less time to waste, have seen a bit of life, made all the big mistakes, and know what they want. Certainly going by all the dreadful catfish stories there are plenty of older/mid-life women wanting to feel desired and wanting committment, affection, sex.
I actually don't think the OP would necessarily find it too difficult to meet and find another woman. The fear of change though, is another matter. And after being in a sexless relationship for decades your sense of self and your desirability has probably taken a severe beating. That might affect confidence in feeling able to leave and attract other people.
But after thinking about this a bit more and reading the further replies, I conclude that staying is effectively it's a refusal to accept the marriage is over.
If were decades of emotional unavailability we were talking about, most everyone would think it best to leave. I find there's a weird thing about sex that ring fences it from legitimacy as a reason to walk away for many.