They are most likely showing his appearance during The Clone Wars. I don't see Disney reviving him, at least not in Canon.

I have an idea. Although unlikely, I think they could make N-K Necrosis canon.

They are showing him attacking the Nightsisters during TCW. Morgan Elsbeth was a survivor of the Nightsister purge.

^^

This is most likely during the time when Grievous attacked Dathomir that killed all of the Nightsisters

So basically it’s a flashback

As others said it's probably a flashback...

Ok thanks

He literally got shot in the lungs, no way he’s going to come back now, so this is just a flashback.