First and foremost, I'll assume that your game world does not have either cyberbrains, or re-sleeving or download your brain into machines. Otherwise, clearly you have conquered death and "killing" is not a crash with some data lose. With that in mind...
Yes, it is a terrible idea! You cannot (should not?) relive the past.
She was a great villain with a great story's start, middle, and end. She had her part to play, and it was an awesome part. She's gone now. The End. So, bringing her back would, in part or wholly, invalidate some of that epic story. It might well tarnish those memories. This is what comic books do all the time: No matter who dies (Superman? Jean Grey?), they will be back in a few months' time. All that it does is kill death. It makes death irrelevant, something else to shrug just like bad weather.
In addition, your players might well see her for the GM's pet NPC. That is a really annoying trope. No matter what the character do, the NPC will be back more powerful than ever in the next adventure. So, why bother at all?
I get that you want to relive the wonderful adventures you and your players with said NPC. But it generally does not work. It mostly turns into a pale imitation of the real thing. Let her rest in peace.
Some sequels do work...
What if she was not the bad guy again? What if you could change her role in the world?
What if the characters were to find a clone of her: same skills, same basic nature, but a blank nurture. What do the characters do? Maybe she's the one that needs protecting against some other villain? This lets the character bound with her new self, maybe a romantic liaison, maybe they become friends, or she save their lives? Here you have an interesting theme of nature vs nurture. You have added something to the character but let's face it, she is no longer the one that they met before.
Now, maybe the character come to the slow and painful realisation that the true villain manipulated the first clone (!?) to turn her into evil. It's up to the character to turn her from where her nature pushes her to. Who is that evil villain? Will they even hear its name? Will they even met them?... Think Sauron in the Lord Of The Rings: omnipresent all the time, does not have a line of dialogue!
Look at successful sequels in both literature and film industry: The best ones are the ones that do something different, not do the same thing again.
Finally, isn't the root of the problem more about not having time to come up with a new villain?...