*IF* (and that is a big if) that were to happen, it seems rather likely to me that the various publishers would allow us to move our CD Keys from Steam to their DD platform before losing them on Steam, much like how EA allowed me to register my Mass Effect and Sims 3 CD Keys on Origin. As I feel no particular loyalty to Steam, I'd just get whatever download manager I need to play the games I want to play and not worry too much about it.