Kane isn't captain. ;-)
I think I more or less answered your question in my last post. Modric was desperate to join Chelsea in 2011. He wasn't allowed to. So he stayed and had a brilliant season before joining Real Madrid the following summer.
It's up to those that matter at Spurs to determine how Harry would react to being denied the chance to join City this summer. If they think that he would maintain his standards despite his disappointment (and everything that I know about him suggest that he would), then why wouldn't they keep him?