Hux could kill him. I think no point speculating and just watch I guess.
If they want the Reylo approach then a new villain has to come along beating anyone and doesnt gives a damn you are dark side or light. Kylo probably looses mum and she tells him to work with Rey as dying wish and save the galaxy. But I dunno, make it even more emotional then it would be Rey discovering she has enough power to stop the villain but not enough to kill and Kylo sacrifices himself to redeem and dies, end of episode Rey is pregnant. Typical fantasy ending. lol
JJ is to be blamed slightly for not giving direction and mystery box style. In fact the three episodes should have been written and set not wing it.