This would also mean that your friends would reduce their private beacon pool since they don´t get their plots back until you´ve freed up some guild-plots. This system does not ‘gnerate’ any plots.
Maybe a 24h timer could be introduced before a guilds gets “auto-closed”. So that the guild leader has a chance to reduce the used plots in and adequate amount before the guild gets shut down.
Anyway, this is merely a rough suggestion I wrote up in less than 10 minutes so please don´t go into detail with it.
I´m sure that the devs would think about all those cases and find a solution for them if they´d decide to adapt the idea of my suggestion.