In my opinion, the Tama-Go is hugely lacking without gotchi figures and Tamatown.
Tamatown really did nothing for the Tama-Go except give you the ability to transfer gotchi points from / to Tamatown, but that's not a particularly useful feature. There were no transferable items, and because the item system was nearly completely removed in the Tama-Go, it takes away a lot of the goal and play time. Without figures, I can only go on for at most 10 generations without quitting out of boredom.
So, in my opinion, the Tama-Go is certainly not unusable since Tamatown has been removed- but there's not a great deal to do on it anyway, so it's not much of a loss. Your experience may be different, however.