They don't go out after Memorial and "celebrate." They just go home and turn on the TV like every other night. I am not aware of anyone that ever invited their Witness friends over to their home for a special Memorial Evening dinner.
I have to respectfully disagree here. As I got older, more and more JW's would go out to eat and socialize after the Memorial. Some would invite a group back to their home for snacks and association. Others here can tell you that in some congregations, the wine and "bread" would be taken back to the home of one of the elders and enjoyed with cheeses and fruit. There were plenty of us that got together after the Memorial for socializing, whether over finger foods at someone's home, or a full meal at a restaurant. In fact, after my very last Memorial, a group of us that included an elder and his family, a ministerial sevant and his wife, a new "bible study", and some single brothers and sisters all went to a local chain restaurant and stayed out until about 11:30pm enjoying each other's company and talking about the Memorial and other stuff. It was actually a very fun time, lots of laughs and joking, and a "joyous" occasion. I know of quite a few in every congregation I've been in who do at least some little gathering after the Memorial...and I've been in approximately 13 different congregations across the US.