Relics are based on season. So yes, it WILL be set to +0 when said season ends. In Korean version, it was reset when they got 8.2, and Relics changed to new Lords (Kaisinel to Nazekan, Marchutan to Zikel)
With that, there's new rewards, like lvl 100 relic gives fighting spirit weapon box. More info https://aionpowerbook.com/powerbook/8.2_Update
So if anyone plays the game casually and wants to get FS weapon someday in the future without having to run Heart of Apsuranta, they might as well start to save up relics for it.