None of those players you mention are negotiating their contracts around other clubs though are they. Lord Imperial Ferguson had no problem with offloading his top scorer Van Nistelrooy when he started upsetting the apple cart, or Beckham, Ince etc. before him. I think the same is applying here...
I'm personally not questioning Murray's ability per se, but also not suggesting it would be the end of the world if he left. I think your assertion that he would weaken the side more than any other player is wrong because this side is set up (as others have said) to create numerous chances in...
Barnes played 7 less games, and made 6 more of his 38 appearances as sub than Murray did. Murray 0.49 goals per game, Barnes 0.53 goals per game....
with none of the histrionics (but a lot more attitude!)...