He doesn't like being on the wing and it limits his influence. However, if RvP got injured then we'd be delighted we got him. If we sell Hernandez to At. Madrid for £15m~ and buy Cavani for £30m~ then that would be a good move, assuming his wages aren't ridiculous (they probably are given it's PSG and all).
Di Maria would be a far more useful player for us to get, as LvG would prefer to play a 4-3-3 system but it's not really possible with our squad due to the poor balance. We'd need a few transfers in and out to change that though. :/
Looks like your going to play 5 at the back though unless you sign a top top defender to sort the back 4 out. Cavani is a good player i think, proper misused at PSG for sure..he'd be a great signing for you if you can get him for the right amount