I had two thoughts:
What if Argo City goes into the same disruption that Mon-El went through last season and ends up in the 31st century? They all live, Kara finds a way to time travel (Hey Barry! Can I get a hand?), and is able to visit them often.
I don't think it makes Alex pathetic; but I do think the whole concept came out of nowhere and was shoehorned in to justify the breakup with Maggie. It was clumsily done, and wouldn't have had to be done if they had checked with the cast member to make sure she wanted to stay on the show before having Alex propose to her.
Second thought- Could Serena be creating Doomsday? We know she's influencing Sam, maybe she's also influencing Covill and willing him to go through with the ceremony to become a Worldkiller, and instead gets turned into Supergirl's version of Doomsday.