Mark Evanier has recently posted Rodent Rebellion's premiere on Boomerang USA.  He's also had this to say about the show's future status:

"Season 5 of The Garfield Show consists only of the four episodes of "Rodent Rebellion." There are not nor will there ever be any more in Season 5. We may or may not do a Season 6 but that's still under discussion. Season 5 is just those four cartoons which air as two half-hours."

So there you have it.  While the four part Rodent Rebellion is the fifth season- no more, no less- The Garfield Show itself isn't necessarily over yet.  Even with the recent news of the Alcon movie series, there's still the possibility of a sixth season.  I imagine that's good news for those who want more episodes, especially with the brevity of Season 5.

Also, for those of you have noticed any additional episodes being listed for Season 5 (with titles like "Zapper Dogger" and "Cursed Cat") the words of a certain 1940s radio show, "Don't you believe it!"

"There's someone who likes to post phony episodes titles and descriptions of as-yet-unaired Garfield Show episodes on Wikipedia. This person — and it may be a team effort — is quite clever and has sometimes made up episodes vaguely similar to real ones we had in the works. But his or her are bogus and I'm told some of them have been posted for Season 5 and then deleted like all the other fake ones because they could not be verified. I am the best source you're going to find for this stuff — this blog has been running for sixteen years, guys and my name is on every episode of the series — and I hereby testify under oath that Season 5 is just those four episodes of "Rodent Rebellion." Thank you."

This will apply to the Garfield Wiki as well.  If you see an episode title on the Wikipedia page (as well sources that got it from Wikipedia) and nowhere else, don't bother adding it here.  Even if you think it sounds official, it would be wise to ask an administrator about it first.