The fact that he's still a world top 5 striker (according to me and a majority of the football fans I've spoken to) after all he's been through in a relatively short space of time just speaks to his generational talent.
Let's not speculate about him getting worse over time or coming back worse than before. What's the point? Seems like unnecessary doom and gloom. We haven't seen his medical records. For all we know, four months out rehabbing, relaxing and spending time with the world's best doctors will actually leave him in a better state than he was in before.
There are far too many confounding variables to say that he's finished or even to conclude that he's never going to be as good as he was a few years ago. His injuries have coincided with general downturns in the overall form of the team; he hasn't had enough injury-free time since the start of 2019, which is bad for him as well as leaving him prone to a ton of cognitive-biased analyses; he's looked a lot freer and happier playing for England in the last 12 months and his performances have been fantastic, even relative to the level of opposition (England had the Czech Republic and Kosovo, but made them look like San Marino and Liechtenstein); and related to the last point, Kane immediately looked so much better - as good as he ever did - during some of those early Jose games, which suggests that there's a psychological aspect[1].
And there's still the explanation you always have to look out for in science and logic: that everything that has happened so far has just been plain old bad luck (I mean, I can demonstrate that there's a ton of bad luck involved using the data available to the public.. -- and I've done so before in this thead). Historical events don't necessarily predict future events. In fact, they very often don't.
At the risk of repeating myself, there are far too many confounding variables to say that he's finished or even to conclude that he's never going to be as good as he was a few years ago. So let's wait and see what happens before making needlessly pessimistic projections. I believe Kane has it in him to bring it back but even if he stays at his post-Poch level for Spurs, he's still world class (and if you doubt his ability to make the difference, go back and watch that hard-fought Wolves victory from earlier in the season: Kane didn't even score but he was everywhere doing everything to eke out that win, becoming a solid MOTM candidate).
[1] I don't know why this is the case and my comment is not an attack on Spurs. I don't know what's going on at the club, with the squad, these days, but I think we all realise there's been some kind of general malaise around the place for at least the last year. FWIW, I absolutely believe that Kane is one of the players who still tries hard for the team, but so much of mood and motivation is not even conscious.