They offered him a contract and he has a chance to go deep in the playoffs (especially in the East).
Signing at minimum allows their new team to acquire more depth. Adding all of the above for a combined 7 million cap hit? Or even 2 or three of them (Sedins + Vanek = 100 goals for <$2mil combined)? These players are already set for life, one season making "only" a half million won't kill them, but will drastically improve their chances