Tommen too much of a pussy to strangle anyone.
I don't know if Margery will get killed but Cersei definitely wants her punished, that was the whole point of all this in the first place before it backfired on herself. Something will definitely come down to Tommen disagreeing with his mother and siding with his hot wife (lol what teenager wouldn't!?) and shit will go down, I like your original prediction Zombie Mountain crushes him, Hound kills Zombie, chokes Cersei to death while dramatic scenes of a helpless Jamie is restrained, watching his soulmate and sister die before his eyes moments after watching his son murdered by the beast sworn to protect Cersei.
So here is my recap of our discussions and a couple added notes, because I don't feel like working but typing a lot makes it look I'm a hard worker:
One thing about Bran and his storyline, I will say this about Bloodraven. He's a very unique and mysterious man. I've read the dunk and egg books as well, and pretty much everyone who talked about Bloodraven spoke about him in a dark, negative way. Of course this could just be the perspective of the common folk and others, depending on what house/region you're from, but I certainly got the impression he was a bad dude. Obviously that was a long time ago so whatever happened to him, perhaps it changed him to be "good". But I still have a suspicion he's up to something...evil.
I have a couple of predictions in my head and now in combination with Butchers ideas with Cersei. We know her childhood prophecy of losing three children and "valonqar shall wrap his hands about your pale white throat and choke the life from you." and some people assume valonqur is little brother so they figure at some point Jamie is going to kill her. What I'm thinking though is that whatever she has cookin up, will end in trail by combat, and of course Zombie Mountain will be her fighter and the high sparrow will have the hound (so this would also have to believe the fan theory clegane bowl is true). Here's where it's interesting though, The Hound is the younger brother to the Mountain, so he could be "valonqur". Perhaps at some point during this, King Tommen will defend his queen Margery over Cersei and since Zombie Mountain is sworn to defend Cersei, he'll glitch out so to speak and crush Tommlen. The Hound will kill his brother and choke Cersei to death. Prophecy fulfilled. Very dramatic finish with Jamie unable to save his sister!
keep an eye on Littlefinger. Ramsay's letter to Jon in the books is a bit different and happens earlier than the show and there is great speculation if he even wrote the letter. In the show it seems cut and dry, Ramsey wrote it, that's it. Both versions of letter though Ramsey or whoever wrote the letter says "come and see" multiple times. With that said, earlier in the episode when Littlefinger gives his gift to Robyn, he clearly says "My lord, come and see". Now this could be nothing at all, a massive reach, but it could also be a subtle clue that Littlefinger either wrote the letter or is at least going to somehow support the Bolton's. Remember, his true goal is to be Warden of the North and more, so he most certainly wants a war, a bloodbath, he wants each side to decimate each other, and he certainly won't want any Starks alive other than Sansa, so he can then swoop in for himself and claim Warden of the North, so expect some double crossing manipulative stuff from Littlefinger (as usual). This of course could be his demise too, but it would certainly complicate matters and divide the North.