I think Stan will be first to leave, I love stan though and hope to see a bit more of his nasty streak like in the first ep. You can already see that he is controlling Dean and the rest of the Carters.
Unless Danny leaves or they do an 'affair story', I can't see Linda (Kellie) leaving without him.
Dean will probably stay a few years but I can't see him long term.
Lee will remain recurring, I'd imagine.
I can see Tina and Tosh leaving within a year or so also.
Mick is a tough one, I know Danny says he wants to commit but I'm not 100% how long that will be for. Hopefully for quite some time.
Shirley, I think she will stay quite a few more years and be moulded into a Pat figure, well I hope so anyway, I like her having a family.
Nancy/Johnny/Aunt Babe, I'm not sure on those, I hope Aunt Babe stays for a long time yet though.
The Carters have so much potential so I think they will all be around a while yet!