He's proving that he deserves a future here imo. Whether that's as a squad player so what.. he's versatile enough to warrant persisting with and he's actually performing in clutch scenarios. Happy for the lad.
I actually differ a bit, Lingard has a role to play and that role is playing off a main striker, someone who holds the ball up and lets Lingard run and find the space.
You'll notice that a lot that Lingard's weakness's are exacerbated because of the midfield role we've continually asked him to play. His striking technique, finishing and ability to find space is almost second to none in our current squad, add to that the fact that he'll press from the top, I'd wager he'd make for a brilliant supporting act to a hold the ball up striker.
While this might sound like a football manager-esque rant, there is a vital difference between the #10 role our formation has and the support striker position that I explained above. The #10 in our team would have to shoulder some creative capability, finding the right pass for Lukaku or Martial/Rashford to run on to or even to switch play when it gets too crowded in the middle.
Having Lingard play there or on the wings would cause concern because Lingard isn't the best at finding the right pass or even if he notices it, he doesn't execute it with the frequency expected off a #10 for a top side. However relieve him off these issues, probably get him to run onto the ball and finish it you'd have a brilliant player with atleast 20 goals per season in him.
As ludicrous as this sounds, you'd have him posting Rooney like numbers if you put him in that Rooney-like position.