We can't say that yet. Harry Kane is a good palter and even as a 31-year-old player he had good performance in Bayern Munich and any team he played for them. I think Harry Kane can even have the chance to play in older age while being in the good form just like what Ronaldo is doing while is old.
But still, Harry Kane can't be a long-term investment for Bayern Munich.
I think Bayern can find his use still for 3-4 more years in my opinion. He is a top striker and Bayern have invested a lot in order to get him. Naturally they will use him for a long term and they certainly have bought enough time with this also for finding a young striker filled in with good potential. I think in 2-3 years Bayern will start looking for next striker.