I don’t think there is a proper way to compensate this with gems. This is rather something you compensate with “features”, something players would not be able to obtain under normal circumstances. Hand out a free campaign pass, put all tarot cards / egg dragons (at standard cost) into the forge for a couple of weeks, remove the paywall around the ancient event weapons and add them to the crafting rotation, stuff like that. It also can’t be measured with gems, and it feels more like a realy apology for what happened.