In that circumstance your points will not expire, and there is no need to transfer until you need them. (This assumes that both cards are linked to the same Membership Rewards account.)
I was talked into getting a Premium Gold (or whatever) AMEX and the existing Express MR points (from my Optima account) were folded in and converted to regular MR points.
So now if I cancel the Premium card (but retain the other card), will they remain regular MR points, or will I lose/down convert some/all the points?