It's more complicated that a straightforward "should we have sold".
For years and years of having our best players sold with us as a stepping stone, we haven't done that. Even Walker went on our terms to a degree and none of us thought losing him for a fee of £50m was a bad call, really.
Selling your best player, who could yet still reach higher levels (most goals and assists last season) for a paltry £100m with three years left on his deal? We all would have been furious. All of us.
In hindsight it looks a mistake, but has he fallen off a cliff and lost ability? Have those injuries taken their toll? Does he just not give a shit? These are all variables to consider.
If he's shot, then obviously it's a mistake and we should have sold him, but we will never know how much City really wanted him, given the reported £75m + extras offer. Trying to reactivate discussions in the last week of the window when we wouldn't have been able to get a replacement was a non-starter too.
Obviously the way Kane is playing is only going to decrease any future fee too, but also opportunities. If you ran a business and you were looking to hire someone, this is his interview: would you hire him?
He's been badly advised, continues to be badly advised and isn't doing anything to appease anyone.
Bottom line, he signed a six year deal. With no escape clause. He was happy to do that at the time, he wasn't forced to.