Kinda depends... they would have had a little over $8M to re-sign Robertson if they went with a standard/conservative 22-man roster with the cheapest filler options. But if they want to keep 23 and further if they want to accommodate some of the young guns who are a tad pricier than some of their filler options, then it would eat into that a little bit.
Moving Cap would benefit them on the the Robertson front, certainly. It wouldn't have been impossible to sign him for 8x$8M-ish previously, but if they have decided they truly want to keep some of Johnston/Bourque/Stankoven and also run a full 23-man roster, and that they are willing to lock up Robertson at more of a "premium" price than a "fair/bargain" price... then yeah, they would need to move Cap. And giving up something to get rid of Khudobin is the easiest way. I imagine they hoped Khudobin would fail his physical or something. But if that ship has sailed, their hand might be forced now.