May have done terminal top end damage.

Follow Steve C's advice for a rough idea, but you'll really need to pull the cylinders off to get a proper idea of what's going on.

You might be lucky in that it didn't seize, but you'll need to check the flatness of the heads as they may have distorted. Also worth looking closely at the bog and small ends. Any signs of discolouration? This is not a good thing and means they've overheated and could possibly be out of round. Dothe bearings show any signs of blueness?

In the best case you'll probably find that the heads have warped a little.

The NSR doesn't like to over heat. No two stroke does, so don't take a water leak lightly. If it leaks then stop.....fix it....and go out and play again. Cheaper and much less frutrating than having to pull it apart.