Prior to such a case where a creature's soul has been harvested by Thanatos or an Azreael, a creature is completely free and able to be revived, within the appropriate time frame, as dictated by the spell. On casting, the creature casting the spell must make a base skill check of DC 10.
If the creature has been revived before, or a revival attempt failed, the DC increaes by 2 for each attempt.
As part of the revival, up to 3 people other than the caster can assist with the ritual to revive the dead. These characters must declare exactly how they're intended to help with the revival and the DM determines the check necessary to assist. The Resulting DC is equal to the revival DC. On a success, the revival DC decreases by 2. On a failure, the DC increases by 2. A Natural 20 and Natural 1 count as 2 successes or failures respectively.
A spell of 1 action or less does not allow for assistants, instead making a standard spellcasting check against the revival DC.