Question on this position (Kasparov vs Topalov 1999)

YouTube

I don't know the move number, but about 20:10 into the video.

Topalov plays Qxd5 to prevent mate.

It appears to me Kasparov could have followed with Kb2 creating an quick unavoidable mate. But he's Kasparov so clearly I'm missing something.

Nevermind I think I found it. Topalov can then force a Queen exchange.