My ex missed DS2's birth because it went from them telling me I wasn't yet in labour, to him coming out in about half an hour. No matter how hard he tried, there was no way he was getting there as I'd had to change hospitals from the one close to home to one 40 minutes away because after some health issues, my pregnancy had become high risk.
Anyway, he arrived about 5 minutes after the birth. He called me to find out where I was and it was kind of cool because I said "I'm in delivery, um, I had the baby." I was worried he would be sad about it, but he wasn't. I didn't really mind at all tbh, we got to spend time alone with DS2 after that, and that was really nice. The labour was so quick that I don't think I'd have noticed who was there. I'm sad that my photographer didn't make it, though.
Anyway, sorry for the essay. In the circumstances you posted in the OP, I would be annoyed. Missing it for a legitimate reason is one thing, but if you miss it because you fell asleep then you're just an a$$ IMO.