I wouldn’t sell him. He matured his game a lot with us.
About replacing: Verdi?
I would only sell him for a legit offer of 80M +.
If Suso was at Barca or Bayern he'd be an absolute star. We're lucky to have him. I think though, another year like this next season Suso and other's would probably want out.
For 80M, I'd try for Chiesa as Suso's replacement at 30-35M. The game Chiesa had the other day was brilliant, a pity I don't think he plays LW.
I'd then use the other 40M to try for Forsebrg, Brandt or Draxler for LW