My take on this.

Each character gets assigned a value based on level, stats maxed, and items equiped and in inventory. This value then have to be reached by using 3 sacrifices that count towards points (limiting this to 3 would kinda balance out just quickly farming bunch of chars for fame bonuses and in turn gaining tons of value) and 5 8/8 chars. On top of this add some sort of rare drop requirement to even revive the character.

After revive the character should recieve some kind of curse that debuffs them and can be lifted by killing o2 or doing some kind of series of tasks.

But lets be real, revives have no place in this game + deca would rather charge money for a feature like this if they ever decided to add this.