I'll split the difference between you and Daps. I agree with you that he should be starting the rest of the season, with Ward on the bench as cover until Key is back. If Sam struggles, then bring Key back in.
In the summer, it all depends on whether we sign anyone in that position. If not, I'm sure Matos will be looking at Parker, Key and Lissah in pre-season and deciding on the pecking order. If Key is third on his list after that (which I doubt he will be), then he should be sold. If Parker or Lissah are third on his list, then they should be loaned out for regular football somewhere. Although the caveat to that would be if it's Lissah who is third on his list, but he also thinks he could compete at centre-back, in which case he stays.
All in all, right-back is way down my personal list of priority positions for signings this summer.