If we tried to replace Baines with a like-for-like left-back it would be impossible. More assists than any other player in Europe's top 5 leagues, free-kick specialist, never missed a penalty and, contrary to what some fans think about his defensive ability, made more tackles than any other Everton player last season. Also, because teams are well aware of the threat he poses, they often try to overload their right flank to nullify the threat, leaving space on their other flank for Coleman and Mirallas to exploit.
If Baines doesn't ask for a transfer, we should keep him and offer him a new contract. If he does ask for a transfer, we should be looking to get a fee at least in the region of Fellaini's 23 million release clause, and then look to spend the money on adding creativity to the team in other areas to make up for the loss of Baines' assists. For me, that means spending a large chunk of any Baines fee on a quality play maker, rather than a striker.