Or maybe kill off the SMALLVILLE Supergirl played by Laura Vandervoort? Or, just to be really cheeky, kill off an older Supergirl played by Helen Slater!
I thought of that too, though my thinking is this--while it's really exciting to bring in all these other shows, the reason to do it is because basically, the fans know them, and have a nostalgic love for them. I think that to bring them back just to kill them off would be disappointing to those that were looking so forward to seeing these characters.
Since these writers are Arrowverse writers, and not Smallville writers or the Salkinds, I think they should leave the guests alone and have them just be heroes.
It sure would be interesting to see Slater suit up, and I wish they would also bring in Dean Cain.
I think what's very important is that the writers not follow the comics to the letter.
The purpose of this COIE is to create an all out amazing event to entertain. The purpose of the comics was to reboot the comics into one universe. We don't need that on TV, and to be honest, I think that's a terrible idea.
Looking back, COIE was unnecessary, which I think is the reason DC undid it a few years ago, and the original multiverse exists again.
We also have to think about the future of the Arrowverse. The writers have an amazing opportunity to make some course adjustments. After all, I doubt when they started Arrow, they ever conceived of so many shows.
If worlds are combined, they should be Arrowverse worlds. So Smallville would still exist in its own universe. Some universes could be destroyed, but it should still be a multiverse.
Heck, maybe instead of contracting, they expand from 52 worlds to an infinite amount (which they kind of did with Earth 90).
If it were me, I would absolutely bring Supergirl and Black Lightning onto Earth 1.