Correct. If we had another equally good player in our team I don't think you can ignore a 60m offer. Alas we don't have that replacement and selling Willian so we can potentially get a replacement as good as Willian is not worth the trouble considering the far bigger holes we have in our current team. You don't just go out and buy 3-4 top players at once (Which we need IMO).
I'm definitely not a Willian "fanboy" whatsoever but I still stand by my opinion that you can be a big team and win with Willian in your first-11. He's not a star but he's not a liability either; Willian's ability to keep the ball and to not make any mistakes leading to us conceding makes him a plus-player worth keeping around. Play Willian with Hazard, Fabregas, and a 3rd creative player (whether that's an offensive fullback or another creative midfielder) and you will see his true value to the team.