I got home from work a little while ago and did a complete water change in the tub. The water smelled as bad as the box when I first opened it. For some (unknown to me) reason there were apparently live plants similar to hornwort packed in the plastic containers, along with wet paper towels. Needless to say the plants didn't survive 2 weeks of total darkness, most were reduced to foul-smelling piles of brown mush. That's the smell I'm trying to get rid of with fresh water now. The bubbling airstone doesn't help the air quality in the room much...
It does look like most of them are alive, though not all of them are active. A fair number are just lying around, unlike the ones that have climbed the sides of the tub or scattered across the bottom. So far I've turned up one empty shell, and there are more than a dozen loose shell "doors" lying around the bottom.
As for the pellets, it's impossble to tell whether they ate any. The pellets have long since broken apart, and 95% of the debris was dumped with the old water. Word is the critters will the same things as other snails if there's no live prey available. I have a fair number of ramshorns and pond snails in a 10 gallon tank, but not enough to feed this crowd more than a single meal. I'll try some NLS pellets tomorrow.