I think if Henderson’s £75k wage demands are met and Man Utd then expect any Premier League club loaning him, to pay 100% of his salary, he’ll be playing for their U23’s next season.
They have to be realistic and look at the benefit, not just for their player, but also themselves. They already know how he performs in the Championship, so what would they learn by letting him go back to that level in return for 50% salary contribution? United have agreed to pay that, but will play him in the Premier League. (I think, as Man Utd have the leagues highest wage bill, they should take into account how his wage fits within the pay structure of the loaning club)
After 36 games playing at the same level as his parent club, they will get a realistic insight into, not only of his current ability but also his future potential, which is surely invaluable to their future planning, given their fragile goalkeeping situation?