The SL22B Castle is big imposing and beautiful and highlights the quality of content that is possible within Second Life. It also has the qualities of a really good central hub and social gathering spot.
I think we should keep it after SL22B. Maybe turn it into a welcome hub where people can socialize or put it as an island on the mainland somewhere fitting, it's a really wonderful asset and it would be a shame to lose it after the birthday is over.