I really want to know how Dean and Sam are going to defeat Lucifer without Dean becoming Michael, and judging par the 100th episode...I need a psychic.

well my sister and i have speculated that they're going to trap and possibly reopen lucifer's "cage" with the horseman's rings. however, at some point if that doesn't work there is no way that they can. the poulain, colt didn't work, i don't think the Angel killing couteau works on archangels, and lucifer is an archangel in spn canon. so.