@Latecomer
As far as I know…
There’s not even evidence that he’s
actually the “spirit of disharmony” or “god of chaos” everyone claims he is. That he’s some primordial force linked to an unkillable concept as opposed to just one of the many magical critters in the world of Equestria, like Ahuizotl or the Pony of Shadows, except that he’s got loads more power.
Could actually be just some random monster who lucked out on absolute power and got drunk on it like Trixie was on the Alicorn Amulet. And whatever happened in
Discordant Harmony (didn’t watch it) was just withdrawal rather than Discord actually embodying ‘chaos’ and so needing it to survive.
For all we know, he’s just a small fish in an even smaller pond and the first hero or villain from a slightly tougher universe who walks by could kill him for good with a slap of their gauntlet. Or even someone in-universe who doesn’t rely on old relics lying around for centuries or feeling emotions
really hard to deal with threats.
So no. No evidence whatsoever about how long he lived before or how long he’ll live after the finale. Unless you count believing everything Discord says at face value as ‘evidence.’ He’s the type to cheat death if he can though.
Will also note that many people seem to get “immortality” wrong. Living for over one thousand years doesn’t mean living forever. Maybe alicorns actually live for 1,200 years before crumbling like a house of cards and then dying and that was one of the reasons Celestia put Twilight in charge.