It's more likely they'll coincide either the end of his next stint - or perhaps a following stint (if he committs to another comeback later in the year) with the return of Sharon after her extended break.
Perhaps a tug-of-love storyline with Grant/Sharon/Phil/Carla
Killing him off would be a waste of money - considering how much the BBC are paying him to come and work for them. They're obviously trying to invest into the character and build it up so he will stay a while longer.
I think his latest return in the spring will lead to the exit of Johnny allen and the return of Phil after his panto break!