Various paired endings have Edelgard/Lysithea "cured" and their lifespan returned to normal. IIRC, it generally involves them being paired with Byleth, Hanneman, Linhardt, or Manuela. A couple others are arguably ambiguous. So yeah, I don't think it's unfair to assume Edelgard could have a normal lifespan in CF though it wouldn't be guaranteed. I think it's most explicit with Lysithea but if it can be done for her there's no reason it couldn't for Edelgard.
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xp1337: Don't you wish there was a spell-checker that told you when you a word out?