I don't see any way in which we sell him in January - I'd have expected some murmurings of potential signings at RB, of which there haven't been any, if that were to be the case. At this point, even if we had an eye on a long term replacement it would almost certainly hurt us between now and the end of the season to replace him.
But to the long term discussion, any player in the squad who is a clear back up should be on the list for potential upgrading. Royal himself is probably at peak value and we'll soon be in a position whereby we have to decide whether to stick (new contract) or twist - in terms of squad building i don't think you should be signing up existing squad players to long term contracts (unless young and/or HG), better to try and improve. I think that's a good rule to have that should see the squad remain fresh year to year.