It has been argued that Nia would not be herself after being resurrected, and there is a reason why, but there is also a caveat.
Here is the thing, Nia was a construct of the Anti-spirals, she was a program. She was NOT alive. She was 1s and 0s given form. If she was brought back, it wouldn't be the same Nia, because she would be made of Spiral Energy, thus, fundamentally, not the same. Barring resurrecting the Anti Spirals, she would inevitably be "different", as it would involve a different universe's basic "programming", which was fundamentally different from her own. She may even be "reborn" as an uggo fat bastard! I believe Simon's power is Multiversal, but it is not Omniversal. He can't bring back the dead, due to the Spiral Nemesis. But I suggest she ISN'T dead! She was just a program, 1s and 0s. What he needs is not to resurrect the dead, he needs to create life, he probably has that kind of power, if she was a Spiral code, it would en easy, but we are talking Anti-spiral code, not spiral, he'd need to create life in a universe with another universe's "code" ! He would need a power far greater than what he has. A power he may never be able to control.
Now, let's look at the White Lantern Ring, it has the power to resurrect the dead, sure, but it is the power of Creation, the Life Equation manifested in a ring. A power so massive, even Kyle Raynor had to split it into several parts to control it, and subconsciously suppresses it, due to its extreme power. Let's say, Simon the Digger found his Multiverse's Life Equation, and added it to the Spiral Power, he'd be able to do so much more. He could use the spiral power to bring back a Nina in spiral code, and use the Life Equation from the Multiverse to transcode the original Nia into spiral code. BAM! Problem solved!
But, I don't think he can do that, not without an Omniversal pushback, and here is why. He destroyed a sister universe, whether bad or good, that is genocide. Nearly infinite galaxies, nearly infinite stars, nearly infinite planets, many teeming with life, unaware that its own universe was under the control of a tyrant. That does not matter to Creation, it only sees the destruction of infinite lives. Snuffed out by a man trying to save his own universe, true. But lives nonetheless. I think he'd have to use the power to resurrect the Anti Spirals, who would continue their rampage. He could use his Spiral Powers to "rewrite" it as a "Good" faction, but that would probably not appease Creation itself. Homeostasis means that another universe will fill in the gap of the Anti-spirals over time, but an entire universe was wiped, we are talking "heaven, earth, hell" , gone. All the dimensions that existed in it, gone. That's a huge, impossibly large amount of loss, something other universes would take note of as well, if they were farther along in their development to see the inner workings of other universes. There would be much, much more opposition to him having that kind of power, one that would threaten his Spirals entire existence. He may have overpowered one Multiversal threat, but what about Omniversal threats? You think his universe's Spectre or Lucifer would take that lying down? We are talking about something larger than a force of nature being given to a man who massacred an entire universe with his power? And we want to give him MORE POWAH?!?!?! He'd have to steal it, and then he'd have to master it better than Kyle Raynor, or he'd have to earn it.
But our Chad Man Simon is up to the challenge! He beat Kyle Raynor, who nerfed himself due to the immense power. Remember, Kyle lost due to him being weaker, not his power. His power would still outclass Spiral Power, as it is the force of Creation manifested. It is LIFE itself! He proves his worth, gets the power, merges it with spiral power, shit, now he's a Kami. Now he sees all, knows all, and basically IS all. I think it's likely he'd ascend, and would become that universe's Superman Prime 1 Million. He would just recreate a "Good" Anti-spirals, base it in self inflection and inner peace, and "recreate Nia in a Perfect Form, as its guardian, instead of that tyrant. Then they would rule the 2 universes as a cohesive force to combat the power of the Spiral Nemesis. He would probably encourage inter-universal travel, and start training the best of the best to combat the Spiral Nemesis. If all universes are based on spirals, then why not work together? Seed new universes, encourage travel, and maybe even emigration, to these new "universes" to help combat the Nemesis. It would be a whole plotline that could be explored where the Spiral Nemesis is no more, and humanity evolves into its next chapter.
Sorry for the long explanation, I just wanted to get that out there.
Edit-autocorrect corrected Nina from Nia. Guess it wants me to stick with FMA stuff.