It will be great to have him back. He is a great character. Sharon was indeed the love of Grant's life. All the others didn't come close. I don't want a sharongate repeat though. However, I think they will always hold a torch to one another. It will be intresting to see how Sharon and Grant react around each other and how Dennis will feel to have her ex-husband back in the square. What ever the outcome though, it's Dennis that I want Sharon to be with.
As for Phil/Grant/Dennis - I think they will bang heads with him. However I don't feel that this will scare Dennis or put him off. He can certainly handle himself and give as good as he gets.
All we need now is confirmation.