Responses
I don't think he is dead, I actually believe he is Dabi (but there is no proof yet, so what I said is what you can gather after reading the story without the knowledge about that theory). If that is the case, Endeavor hurt him so bad he ended up becoming a villain. And if Touya is actually dead, then Endeavor killed him. Either way, that man just ruined his family.
The last page and then the way Natsuo is always acting around Endeavor. I still remember that panel where he says to Endeavor that he is guilty of what happened to "Touya-nii", back when he just got that scar after the battle against the Nomu... So what I can gather is that Endeavor killed his son. His training was so brutal and Touya's body condition so fragile he died because of that hellish training.
Endeavor sucks, man. Like I get it that he is trying to become a better human being, and I believe people can change even after doing things badly, but he killed his son and gave his wife an emotional scar that she will have all her life, because reality is that abused woman never forget the pain and the fear, even if they are capable of live better.
So yeah, I just can't stand Endeavor. Cannot forgive him. I just can't. :(