It's a big surprise for me seeing our fans are still discussing whenever this is a good deal or not.
50 m pounds for a player of Sanchez caliber with 3 years of peak form is already a bargain. The wage, bonus won't make a big difference here since all the players at that level would ask for a similar package.
Mkhitaryan came to us at 26 m pound, I'd hardly argue with anyone who value him around 20 m pound now given the current performances so ~30 m pound + Mkhitaryan for Sanchez is definitely a bargain.
If Sanchez comes, one of those Martial, Lingard, Rashford, Mata, Mkhitaryan has to go. The choice is easy here, even if he stays, I don't see a much game time here for him.
Mkhitaryan is earning around 140 - 150 k/w (not the 200 k/w someone said above), cutting that off will help us a lot in balancing the books once Sanchez comes.
Arsenal if let Sanchez goes would need a replacement. Given their current status and usual transfer policy, I think they'd be very happy with Mkhitaryan.
So overall, it's definitely a good if not great deal for everyone except Mkhitaryan.