Well the season is ending with the Battle of Mandalore, the final battle of the Clone Wars, so they'd have to make any future episodes set before it.
The original plan was to have a few episodes set after Episode III. Plus there are also all those unfinished episodes with Boba and the Utapau one.
The Battle of Mandalore crosses over the end of the Clone Wars since it happen around the events of Revenge of the Sith.
Clearly they *could* go back and do all those episodes that were written or just conceived prior to the cancellation, but I doubt they will. I think how many episodes they do or whether this is really *really* the last season depends more on how much time Filloni has to dedicate himself to this one project over whatever others are cooking, than whether there's any more story left to tell. By all accounts, Filloni is only going to get busier since they seem to be grooming him for live action directing as well as animation,
But some are close to completion. Would be a crime not to. I just really want them to do that Vong episode as well.
What I'm thinking is that we know there are further unfinished TCW episodes besides the ones included in this season. So maybe if Disney's happy with this season, they could go back and finish the rest of the planned episodes, releasing them as a "lost episodes" sort of deal. Just as a hypothetical, though, there have been other shows that continued after their titles ceased to apply, like Blake's 7 after Blake left, or Smallville when it mostly relocated to Metropolis, or Sleepy Hollow when it relocated to Washington, DC. So while there's certainly room to go back and fill in "lost" tales during the war, I can see the potential for TCW to continue beyond the end of the war, telling stories that arise from the aftermath of the war, so that the title would still have a thematic relevance if not a strictly literal one. In real life, often the most important part of a war is what happens after its nominal end, what decisions are made in establishing the new status quo.
I actually wouldn't mind to see maybe like one more arc set shortly after AOTC but before the first chronological episode of TCW. Maybe we'd see how Anakin gets his scar since he already had it when TCW began, and we could see how Ventress got involved since Anakin and Obi-Wan were already familiar with her when she first appeared.
At first, TCW seemed to be implicitly avoiding the ground that the earlier Clone Wars animated "microseries" had covered (including Anakin's scar and Ventress's introduction), as if they were treating it as canonical or at least being agnostic about it. Eventually they ended up contradicting a lot of its particulars, though.
Look at the smiley. Seriously though, I think Dave and Co. could probably reboot them to actually be good.
We know Resistance is ending this season, but I haven't even seen any rumors yet about what the next animated series will be. Maybe we'll get a direct Clone Wars follow up filling in some of the gaps in the survivors' stories between TCW and Rebels and/or the Original Trilogy.
One would assume the next logical show would be picking up the Ezra/Ahsoka/Sabine thread, not filling in even more gaps between the first two trilogies. Granted the above scenario would presumably take place between the ST and OT...but maybe not? Perhaps they could just jump to a decade post ST and have elderly Ezra & Ahsoka helping Rey build a new order of force users? I mean their trip out into the unknown regions was mostly to keep them safe and out of the way of the movies while those events played out. So after tRoS it should be wide open to bring them back.
Those are pretty good possibilities too. Thinking about it more, once The Rise of Skywalker is out, I could see them stepping back from pretty much all of the earlier eras to focus on the sequel trilogy era. I've been assuming that they've been focusing on stuff around the Original Trilogy because they wanted to didn't want to ruin into any issues with reveals that were coming up in TROS, but once it's out that won't be a problem anymore.
If they plan on having one come out after Resistance ends, they've probably finished writing the first season already. Considering how long animation takes and all that. For example, they started Resistance Season 2 in 2017.
They should do something completely outside the movies for the next one. Set it hundreds of years before or after them.