If want forever no fade, you have 3 options:
1. Doubleshots, it will only fade after you completely wore off the keycaps(which will take at least hundred years of use...)
2. Dye-sub, similar to doubleshots but as it is PBT keycaps, it will took you even a longer time to wear off the keycaps and fonts.
3. Black engraved keycaps, basically there is nothing for you to wear off on them.
BTW, try contact imsto if he got any lasered PBT keycaps replacement for you.