Ignoring that most recent tweet about him signing a new contract, I don't think the motivation will be there for Spurs to sell him this summer. Kane has guaranteed them 20+ goals per season for many years now, and Spurs are much, much worse without him. The powers that be over there may weigh whatever transfer fee they are likely to get for him versus having another season of him and then planning their next move for when he leaves (Or the small chance that he renews during that time again). Realistically, let's say they get 100 million for him, who can they get that will replace what he brings to their team with any certainty? It is a big gamble for them, and I can see a lot of reasons why they may prefer to keep him for one more season rather than sell him.