Country: Iceland
If you wanted to sell him because his legs had gone in the sense that he's not quick/fit enough to last, I strongly dispute that. He is technically and mentally brilliant, if fit he comes straight into our side and we are a far better side for it.
If you wanted to sell him because his legs had gone in the sense that you felt his body would fall apart, I don't think that is very realistic. Imagine Wenger coming out last season and saying that despite being fit, we are selling Santi because we are worried he'd get injured again. Fans would have lost it, he's that important of a player and that hard to replace that you roll the dice in that situation every time.
The issue with Santi has been that no one else stood up in his absence. Xhaka, Elneny and Ramsey have all been average, that's been the problem. If just one of those players actually stood up, we wouldn't be so dependant on Santi coming back.
I wanted Santi to be sold because he was old and suffered harsh injury in the season before. I thought he would have better chance on prolonging his career in Spain/Italy.
I'm also zero fan of Coquelin-Cazorla partnership and not a fan of Cazorla as a deep midfielder at all.
I'm asking again, do you want to rely on him being fit for most part of next season?