The employee took a risk accepting equity as part of their compensation, especially at a pre-IPO company. Zynga shouldn't be able to come back, with 20/20 hind

The employee took a risk accepting equity as part of their compensation, especially at a pre-IPO company. Zynga shouldn't be able to come back, with 20/20 hindsight, and say "turns out we did better than we thought we would so we're taking your stock back". If they failed they certainly wouldn't be giving employees other compensation to make up for their stock being worthless.