Yes..Its going to be his dad who pulls him back I'm sure of it..NOT LIZ..IMO the whole thing about his dad saving his sons life 3 times in the latest one is so it will make sense when he does it in the last one...
In my opinion. She's going to choose Jack over him..thats whats going to make him try and do something crazy in the first place, he's going to see that Liz is falling for Jack in the next one otherwise he's not going to go over the edge which would make all the Will/Davy, dad, knife hints in the latest one irelevent.....
If she did go back with him then that would mean she goes back for sympathy of for fear of what he might do if she doesn't and not for real love... the ending kiss would be meaningless if it was with Will ....is that an interesting way to end it?? NO