He surely will make a final appearance but since he's about the strongest Devil (ok besides Dante) out there, by beating him, (mainly killing him, since if he returns again and do the whole "sealing him" thing again it will become a joke since he surely found a way to bypass it before the 2000 years) it will be like the end of DMC. I mean he is the Lord/Emperor for all demons. So if he got beaten the others don't stand a chance.
There's always Vergil to take over though. But since Dante alone could not kill him(Mundus), I'm sure they will need his strength (Vergil's) as well. After all he is the 2nd more powerful devil if he awakes his true powers (like Dante did before he defeated Mundus).
So to make this a bit less confusing.
I think he may as well return. But unless someone else overcomes him (besides Vergil) his final appearance might as well bring us closer to the end of the Devil May Cry series. You know, no Demon Lord trying to conquer, etc. Dante's mission ends by destroying the most powerful devil etc.
So I think that IF he returns the story will be awesome but nearing its end.