Surely we wouldn't have purchased him if van Gaal didn't think di Maria would not fit into his philosophy? Especially, given that we spent £60m on him.
What's going on with di Maria is very similar to the situations Mata and Herrera found themselves in, not too long ago. As it was then, the same ridiculous questions and assumptions keep popping up: will we sell Herrera? Why did we buy Herrera? Mata is not good enough to start away from home, we will sell him. They don't fit into the philosophy. Yet both disproved everyone, and people seem to learn very little from their mistakes. We won't be selling di Maria for £35 or £50 million, players of his calibre aren't available every season. If you visit the transfer threads, people speak about purchasing Bale, a player who's quite similar to our number 7, will he not suffer from the same issues as di Maria? Most flair players will struggle to become accustomed to a new style, but you don't throw them away and buy a new, shiny toy; we'll become the club we absolutely despise. (This rant isn't aimed at you)