As good as Johnson can be (and make no mistake he can be very, very good) on his day, those days are just too few and far between now. Even when he was playing well at the start of the season his game was somewhat limited and he was making questionable (to put it kindly) decisions in the final third. He'll pop up with the odd awesome assist or cross and people somehow suddenly think he's the best in the league again but in reality he's not consistent enough for this current team. His (apparent) complete inability to stop crosses from coming into the box has cost us a number of goals this season.
When was the last time he played well for more than a few weeks? His current dip in form is one thing but he's barely even putting in the effort anymore, which is frustrating. Being completely shown up by a 20-year old in terms of commitment and form. He's one of our most senior players, and one of the highest earners at the club, and for £100k+ a week you really need to be at the very least decent on your off-days and brilliant on your good ones.
I'd be stunned if Johnson got a new contract anywhere near as lucrative as his current one (based on FSG's policies about replacing overpaid, underperforming, older players) and so I don't think it would be terribly surprising to see him sold this summer. I'm not sure Kelly is the answer, or Flanagan for as well as he's done these past few weeks. Both have a role to play here, but I think we probably need two new full-backs, depending on whether or not Enrique can sort his head out.