May the incels will get laid and move on. Maybe the guy who gets rejected will go home and fuck his bot instead of stalking the girl who rejected him.
Doubtful - these actions are driven by emotions, not the need to get off. If it were the latter, they could just jerk off at home today and they wouldnt do these things.
They can say, just fuck the bot in the ass.
They can currently just say "no"... I'm not sure why we need sex bots to save us from being bad at communicating.
Marriage rates will probably decline, and so will total divorces after a while
Again, doubt. If you are getting married for the sake of having sex, then you are probably in some kind of restrictive religion. And these religions will probably tell you that fucking a bot is an abomination. If you aren't, then you'll marry for the same reasons people marry today, and marriage and divorce will stay at about the same rate.