Local Subaru dealer checked out Transmission as best as can be done, with transmission still on Ascent. Dealer said there were no trouble codes showing.
As a precaution, out of my pocket, I had dealer replace transmission fluid (& filter?). Then test drive the Ascent for several days. No problems showed up.
I have Ascent Limited back and I am slowly working up to longer distances from home. Being cautious about current bitter cold weather, and having to sit for a tow should transmission fail.
Subaru Corporation (again not Subaru's fault at all); can not write a letter at this time saying the Transmission is or isn't covered under factory or extended warranty. Subaru Corporation is saying, should Transmission fail, at that time the transmission will be fully inspected and should it be determined the cause of failure is tied back to fluid being drained out, then Subaru can write a letter of no coverage.
As for place that messed up. It seems their attitude is Meh! Basically coming down to: Our mechanic found nothing wrong, transmission is working, and your vehicle is drive-able.
I have spoken with a lawyer about situation. It comes down to wait and see, or take Ascent Limited to 3rd-party and see what their mechanic says. I gave up on 3rd-party route, because Subaru dealer couldn't find anything wrong.
Should transmission fail, and Subaru says it is due to fluid being drained out, thus voiding warranty; I plan to pay to have transmission replaced. Followed by engaging a law firm. With orders to law firm a partial settlement will not be accepted. Only full cost of repairs, lawyer fees, and punitive damages will keep local shop out of court.
Again, thanks to all Replies!