If you're not going to use Sigourney Weaver to play Ellen Ripley one more time then don't use the character at all I'd say. I'd love to see her reprise her role one more time but it's also time for the torch to be passed on.
Such was Weaver's intention with the Blomkamp project. I agree it seems pointless to recast the character, though. Just write a new character.
Perhaps Amanda or Newt?
The latter could happen if the above is resurrected.
Amanda? No. We already know her fate, which means no will-she-die tension in a future story. If she's involved in any adventures, they have to be so limited that they're virtually inconsequential, due to that (admittedly, frustrating) piece of 'Alien Resurrection
' dialogue. Humanity simply hadn't had any meaningful known encounters with the creatures since 'Alien 3
' occured. Those few who knew about and sought it, had assumed all was lost.
Either go with the Blompkamp/Weaver project or set something after AR took place. That's the only way to get a truly fresh canvas back, again.