Is it really a “bad end?” They’re going to get older whether Twi herself ages or not. I think they’d be happy to know they’ll still all be friends when crazy old, and that the world will be in good hooves with sparklebutt around.
@Background Pony #46C4
I’m calling bull on Dash considering dying of old age “fulfilling”. She’d want to go out in a blaze of glory. The older she gets, the crazier the risks she’ll take. She’ll die as she lived, and everypony will speak of her last flight for years to come. You know she’d rather have it that way.
@Background Pony #D2CB
Maybe more than that. Granny Smith was about the Mane Six’s age when Ponyville was founded, and “Winter Wrap-Up” mentions that Ponyville has been doing winter wrap-up without magic for hundreds of years. We have confirmation of an earth pony living for at least two centuries. They might not have done it on PURPOSE, but still, Granny Smith confirmed for even older than she looks.
…I don’t think Rainbow Dash will live to old age. It’s far more likely, as far as I’m concerned, that she’ll go down in a blaze of glory, at the center of a giant technicolor explosion that leaves a crater where once there was a mountain. I think she’d want it that way.