Would love to see Livewire return! Any word that she might?

"I would love that, but I dont see a scenario where he would be needed in an episode."

What about a situation in which Mxy actually helps the Supergirl Team defeat a common enemy (like the original Brainiac, for example)?

I don't think we will be seeing Livewire again.

What about Mxyzptlk?

I would love that, but I dont see a scenario where he would be needed in an episode.

I don't think we will be seeing Livewire again.

What about Mxyzptlk?

I don't think we will be seeing Livewire again.

I would like to see her again too. But then they killed her off so... Wait I forget was there a body? Because superheros have a revolving door in the afterlife. 'Dead' people come back all the time. (Like Alura Zor El or Jeremiah Danvers, or even 'Hank Henshaw') but only if we don't get to see the Dead body.
I think there was a body so probably not, but I'm sure they could still bring her back if they wanted to. Perhaps they could discover Leslie's remains are missing or something to reveal she faked her death.
I'm still waiting for the Silver Banshee to return. There is so much fun to be had with that. Especially since Siobhan's grudge is with Kara, not Supergirl. Before the reveal I thought it would be hilarious to see how Lena would react to a Supervillain targeting Kara. Maybe she would insist Kara have a bodyguard 24/7, and Kara would have to try to talk her out of it. (Actually, she could still do that just to mess with Kara) Now it would be interesting how it would work with Lena knowing and Siobhan not. Maybe Lena will think Siobhan does know, but targets 'Kara' so she can't fight back as effectively, without revealing her powers.
Also Lena seeing what taking a grudge too far looks like might serve as a wake up call.

In the comics, Livewire "reformed" and became a "good guy", and an ally of Superman (and Supergirl). That would be interesting to see on the TV show, too!
Another character (not a villain, strictly speaking) that I'd love to see again is Mr. Mxyzptlk. The "Mr. & Mrs. Mxyzptlk" episode was one of my favorites!
Here's Superman and "Mxy":

It would be nice but I'm not sure if it is feasible since the character was "killed off" in S3 in a battle with Reign. However, as you mentioned, since she is electricity, one can never say never to a possible return at a future time.

The key here would be how to re-introduce her and if the actor is available to do it. My bet is no due to ongoing commitments, but then again, if the timing is right and everything falls into place, anything's possible in TV-land.

I too would like to see Livewire again, but I have no idea if it is planned. I liked Psy too, and would like to see her again. Both were interesting, well-portrayed villains who also proved to be useful allies for Supergirl, which IMO opens up lots of possibilities.