Right we're now in February and still no Merc/Hamilton contract announcement, though surely this situation has to come to a head this month and I think mid-February (15th-22nd at the latest) is when this will be sorted out one way or another.
As Russell (who will get the call no doubt in a no deal between Merc/Hamilton outcome) needs not just a new seat fitting for Merc but considering his height, the car's cockpit itself may need changes made to it so that it can accommodate him and fit him more comfortably, and all of that takes time plus with testing starting mid-March and being at a premium as its only 3 days.
But of course for all we know a new contract may have already been signed, however on the flipside if at this point it still hasn't happened, then Merc right now would be pretty foolish not making plans for Russell driving for them instead.