This is probably an extraordinarily stupid question but if the longevity of super capactiors is limited by the electrolyte evaporating why can't they just be sealed off completely without evaporation they would last piratically forever right?
I am probably missing something very big here
But they are!
Some, anyway. I find a few results for military supercapacitors, although I can't seem to find a MIL STD for them (if it exists). One picture shows a glossy backfill on the component, presumably an epoxy encapsulant.
Mil grade electrolytics do the same thing: either an aluminum can backfilled with epoxy (that always seems to be pink or red, on the ones I've seen?), or a metal can with a glass frit seal on one end and a soldered or swaged seal on the other (hermetically sealed, also dry and wet tantalums made the same way).
No need for high temperatures, solder does a fine job as hermetic seal.
Tim