There is no talk right now about Politte losing his job on Blue Jays telecasts. Essentially, his numbers look alot worse than his performance really has been. Since being named closer, he has saved 10 of 12 chances. One of those was when he was put in in the 8th inning with runners on base in a one run game. His only true meltdown was last weekend at Cincy when he blew a 3 run lead. That performance plus another performance at Cincy a couple days earlier where he was brought in to get some work with the Jays down 9-0 and he gave up 3 or 4 runs has really inflated his ERA. He still gives up way too many homers, but the Jays have wanted to develop him into their closer for some time and I think he'd have to have several more severe meltdowns to lose his job.
Lopez has been great so far this year but he has control issues, and is only a rookie rule 5 pick. He probably isn't ready to assume a closer's role yet, although he would be the favorite to take over from Politte if he got injured or dumped. Another possibility would be that they would try out the illustrius Tanyan Sturtze in the closer's role (he of the 4-18 record last year).
Regardless, I don't think either of those guys are worth picking up unless you're in an AL-only or very deep league. A switch probably won't be made in the near future.