Have you landed and activiated your PR yet?
They usually ask if there is any change in the relationship with your sponsor. You cannot lie about that.
I don't think it's that complicated. I don't think getting PR via your ex is an option.
UPDATE:
I re-read your post and found out that you have already landed ( I travelled to activate my PR).
And you are just waiting for your PR CARD to be mailed out.... Well, then there is nothing you can do. Your sponsor could report you or not.