Its not hurting anyone from being there. Seriously, some of you act like Jessie can't make a new capture without ditching Wobbufett. >_>
Wobbufett can stay because, as said, its not hurting anybody. Its there because its there, its not preventing any new Pokemon from joining her roster.
I'd say there actually is a way that it is sort of doing that.
I've heard a rule that Team Rocket can only have five pokemon and meowth on their team to match up to six pokemon on Ash's roster. That would mean someone's got to go before someone comes in, and if anyone is caught before anyone leaves, I don't see why it should be Jessie, who already outbalances her partner.
Seviper is staying just because it's popular and fills in for arbok, dustox could go, especially after the long loss of its original rival, but it's there for sentimental value.
Wobby is pretty old now, and it doesn't do anything it didn't do a good season earlier. With his comical factor pretty washed up, he's pretty much dead weight who is expected to suck, and does suck.
IThe only time its Counter/Mirrorcoat ever failed is when Articuno used Blizzard,
Yeah, it totally worked against ariados, right?
[sarcasm]
I might change my mind if he at least
once had a succesful win, but he only did that in the beginning to seal his fate really. After that, he's pretty much been foiled.
Though I think I'd be happier to see carnivine leave. That reincarnated victreebel is even less exciting. Though I guess he at least is a better fighter than victreebel, but he just gets pwned in the end.
To conclude, I don't think there's any good reason for him to leave, but I don't think he's all that great to keep.