Ever since Arbok and Wezzing left, all of Team Rocket's pokemon have departed in emotional and spectacular episodes. I was qutie dissapointed that Carnivine and the others left the main cast with so little closure.
The five of them staying at Team Rocket HQ is sort of akin to Ash leaving his pokemon at Oak's but I became less confident for returns as BW progressed. Although with Mewtwo and Charizard returning after so long my faith has been restored a little.
Granted Wobbo is probably the only one who was ever as important as those two, but with all five of them in the same place, I can't see how'd they'd justify a return for any less than the five of them.
Without a return, I feel they've all been cheated, esspecually Wobbufett and Seviper who both had a lot of years on the show.