Continue to draw without restarting the canvas, but...
You can now continue to draw without restarting the canvas at 30,000 sprites, but the alpha channels seem to have issues when the canvas is restarted and makes you draw flat colors, and not watery colors.
To make this work, you can only undo and redo on the white background. It can probably work on other backgrounds, but it's not a high priority right now to fix that.