I don't think Rask getting a long-term deal effects what they do with Subban. Malcolm's 4-5 years away from really challenging for a starting job so they can hold onto him and develop him to be Rask's heir, even if Rask gets that long-term deal.
That said, anyone and everyone should be considered tradeable. Subban, Spooner, Koko, Knight... Pick your binky. With regard to Subban, Rask is young enough that you could move Malcolm and draft/develop another potential replacement, if there was a deal out there you had to make.