Well he's gone from Walford playboy to grief stricken widowed father of three. I can see EastEnders focusing on the emotional side of him at first. He will fall apart and I imagine another Walford lady will step in i.e. Honey. I can see Honey and Jack becoming an item, with Honey leaving Billy for a time. This will lead to the Mitchells turning on Jack.
Dot will contact Charlie to return to Walford I think.
It is only just that little Matthew be reunited with his father, who was kept away by Ronnie. And in this regard, I think Ronnie's sins have to be revealed. Perhaps Dot finds out finally what happened to Fatboy and what Vincent did to keep Charlie away. This would devastate Jack but he's no right to keep Matthew.
Jack I think will become a bit meaner for a time, bit more ruthless in his business dealings. I think he will evict Whitney and Lee from their flat. He won't be interested in their problems. And it could end up that Lee and Whitney are homeless, though I don't see the Carters leaving Lee on the street, despite what he revealed to Mick tonight.
There is some scope for story for Jack yet I think.
My worry is Billy becoming the loser again, if Honey leaves him to be with Jack. I've loved Billy's forward direction as a character in the last while, so I hope he isn't regressed if Hack happens.