If the seedlings were 2ft or more high, it's likely they will resprout from the ground next season. Animals do love sassafras, rabbits, too, and especially in the fall and winter.
Often what looks like a seedling is actually a sprout coming from the original tree's roots = root sprout or a sucker.
Commonly, you can start new plants from root cuttings, but it's too late to try now. It's usually done very very early in the season when the ground fully thaws. Half to one inch thick roots, cut 3-5 inches long. You could also sever some of the tree's roots in the ground and leave them right there and they might sprout. A caution here is that you might end up with a lot more unwanted sprouting. (The same thing can happen with severe pruning of top growth.)