NaS, S754 should stay alive (mainly with Sempron) until a shift to M2 (for Sempron) becomes feasible (quite a few factors to consider, but expected to happen mainly in H2/06). The socket unification will happen on M2.
I think Socket 754 will eventually go away, and be replaced with M2, but the key word is eventually. I think it will linger on, and AMD will continue to provide it for the low end business.