With the greatest of pleasure, I have managed to restore all function to my copy of Corel Painter 2015. For future reference, if Painter drops out again because of a Microsoft Update, here is what I did that worked:
1) Make sure Patch 1 and the .Net hotfix are installed
2) Press SHIFT while booting Painter to activate the software switch to return the application to factory mode.
Simple as that.
Oh yeah, and I spent the day with Painter sketching out this science-fiction heavy cargo shuttle, which I am now calling the Sky Reach. It's adapted to carry hexagonal-prism containers. Hexagons are hard to draw in perspective!