I think others have answered this, but I’ll add a bit.
There are no separate instructions for when the entire guild has been inactive, it works the same. If the Guild Leader is away for 90+ days, then those in rank 2, 3 and 4 will have the option to take over leadership.
If there is no one active in that rank, or even no one in that rank, then the guild cannot be dethroned.
Is GM Game Master or Guild Master? There are no Game Master’s on the forum, but if you are referring to one of the Support Forum Agents like myself, the only time a Game Master may be able to assist is if the guild was previously dethroned and that new leader has been absent for 90+ days. If the original leader is still in the guild, usually in lowest rank that the system placed when swapping out the new leader, we may reinstate them.
That does not apply to any other character in the guild.
Sorry, we cannot. Adjustment of ranks outside of what I described above can only be done by the Guild Leader and officers with appropriate permissions granted by the Guild Leader.