Guild rights loose
Here we describe briefly what you can do if you are in a guild but the founding member of the guild leader is no longer there and nobody has guild rights.
Guild Admin loose
A guild without guild rights is difficult to maintain, especially if the guild founder member is no longer there because he or she has left or been deleted and no one in the guild has any rights. But it is not hopeless.
You could of course leave the guild and form a new guild and ask the members of the old guild to join. And then report the guild as 0-men Guild so that it will be deleted.
Get full admin rights
The probably easier way would be to open a Support Ticket in the MoonID portal and get guild founder rights there.