That engine; however, is not worth 200k a week for another 5 years. I would give him a 2 year extension at best on those wages. The issue Herrera has (and why I think United are letting him go), he's at best a 15-20 million pound player given his age and ability. We turn that into a 5 year Contract on 200k and we're paying him in excess of 50 million and he'd be very difficult to move on, on those wages.
In essence, by letting him go on a free if that were his demands, its neither a net loss or a net gain. He's at best worth 150k a week and thats being kind over the next 5 years. Which equates to roughly 30 million.
50 million (over 5 years) - Claimed worth
30 million (over 5 years) - Arguable actual worth
Difference (over 5 years) - 20 million
20 million - Arguable transfer value in current market (United lose 20 million by letting him go on a free)
So United are in a position of - over pay a player 20 million over the next 5 years or lose 20 million now and get on with life without the head ache of another person that will more than likely end up on the bench for 4 of those years... Lets not also forget the potential resources he would consume during that time period (if you think that shit isnt budgeted, think again).