The arrowverse versions could come back since Superman and lois is not in arrowverse's prime universe. So that universe would be different but similar. So the actors can return, maybe even saying the arrowverse had similar story for the twins getting powers, but other major things would be different. Kara would be around to help with a lot, so a lot of the timeline would be different in arrowverse but have same actors reprise their roles while playing the characters differently from Superman and lois. John and Jordan would be slightly different because things would be different, having grown up having an aunt, learning Kara was Supergirl probably leading to clark telling them sooner he's Superman, kara helping against Clark's brother, bizarro universe, and luthor. So things would be different but they can reprise their roles technically as arrowverse versions in a multiverse story.

I have only one issue with the idea doomsday sacrifices his heart for Clark. The fact not only he's from bizarro earth, making his organs be on the opposite side of the body, but also i am certain his heart definitely got bigger and differently formed during his many mutations so the heart could keep up with a massive beastly form. So while yes it's a nice thought, i feel like the ending will not involve Superman gaining a mutated giant bizarro heart as a replacement for his own. They might use his DNA to find a way to extend his life or keep at least some of his powers, like his strength, speed, xray vision, and healing, the only powers that aren't opposites of Clark's.

It's not that big a deal considering how Kara did it in Supergirl this way too, telling the world by having an old friend be her interviewer, Ms. Grant. And here Clark is doing the same thing with his friend and firmer coworker, who's Jimmy's sister. I get this is kinda big, but even in comics Superman's had his identity revealed before to the world. We've only seen this in live action twice though, with Kara in Supergirl and Clark in Superman & Lois here. My point is, this isn't as groundbreaking as you make it sound, it's happened before. This is more like a two feet down in the digging than it is the initial breaking of ground, as it were.