Ok, so having the same problem, and I REALLY needed to delete an etp instance (so it wouldn't get indexed), I figured out the following manual process (assuming a single page in this case):
phew! the question is, where to automate this - SO ugly to do it specifically in site-map/instance-delete... if we don't want to do cascading, maybe we make a new naming standard for an "instance-destructor" function which could be run (if it exists) by site-map/instance-delete
if someone important (ie. not me) decides how it should be done I am happy to implement it.
Do I win the record for number of posts on christmas eve?! (noticing the time stamp tells me there should be a user_timezone preference...)
...the angel said to them, "Do not be afraid, for behold, I bring you good tidings of great joy which will be to all people. For there is born to you this day in the city of David a Savior, who is Christ the Lord. And this will be the sign to you: You will find a Babe wrapped in swaddling cloths, lying in a manger."
And suddenly there was with the angel a multitude of the heavenly host praising God and saying:
"Glory to God in the highest,
And on earth peace, goodwill toward men!
Merry Christmas everyone!