From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Future Pu-erh was one of the unfortunate ones to witness the death of Future Son Goku in 766 Age. In 767 Age, the Artificial Humans killed all of the Z Warriors with the exception of Future Son Gohan and Future Trunks Brief. No doubt the death of Future Yamucha weighed heavily on Future Pu-erh's mind. Along with Future Turtle Hermit and a few others, Future Pu-erh was forced to live in a submarine.