My answer for this question comes from the scene in Eclipse where Jake and Edward are talking in the tent will Bella is half asleep...
Edward says he's considered the fact that in the end Bella could choose Jacob instead of him-Jacob then asks him what he would do if she did-Edward tells him that he would always be "waiting in the wings" because like you have pointed out Jacob might imprint someday. And Edward says that he will always be waiting for when Jacob does imprint for his chance to get Bella back.
So overall, I Bella and Jacob ended up together but Jacob imprinted on someone else, he would leave Bella for her and Edward would come to Bella's rescue...
HOPE THIS ANSWERS YOUR QUESTION
Thanks
Teampotter