To and from my recent New York City stay, I took the new MegaBus route from Amherst. It started on December 15th, departing from Hampshire Mall in Hadley. On the way back, I had arranged to be picked up at the mall, but heard another passenger talking to the driver at one point, and the driver said he actually drops people off at UMass as well. Apparently they aren’t allowed to stay at Haigis Mall for very long (probably because Peter Pan doesn’t want its competition in so convenient a location) but they do swing by there after the mall to drop people off. They may pick passengers up there too, but I’m not sure. It also may be dependent on who the driver is. This driver said that they’re still working out the kinks in this new route.
Hope this information is helpful if you’re planning on taking the MegaBus to or from New York!