Mine has been in for 6 weeks, still in the exact same place I put it to begin with using only the factory attachments. The seats have been up/down 10 or 15 times...
Realistically, if you were to migrate to snaps, would only be the top corners of the back of the seat liners, so your leak would have to happen when the seats were down...You could put a small o-ring around the snap in the mat before installing it, if you were concerned.
Reality is, unless you want 2 different cargo mats, one for when seats are up, and one for when they are down, you have no other choice, other than don't protect the back of the 3rd row seats. If you anticipate most of your cargo hauling w/ the seats up, then the main cargo area mat that comes w/ the rear cargo area mats does the majority of the work...
As for concerns about warranty on the interior...there really is nothing in the zone of the top corners of the seat back covers, I would have no concerns w/ a small screw to hold in a snap there...and if mine start falling down, that is what I am going to do.