My concern with options 1 and 3 is that guilds can effectively hold players hostage.
People will abuse it. For example: inviting unsuspecting newbies to a guild and convincing them to donate their beacons.
I suspect that either of those approaches will be a nightmare for GMs.
Here’s an idea for making option 2 (players take their beacons back when leaving) more palatable:
When a player leaves a guild, they receive their beacons back after a delay (day? week?). This gives guilds warning to adjust their beacons or have more beacons donated. If they don’t in time, beacons are somehow (randomly?) chosen, removed, and given back to the player.
Also: any unused beacons could return immediately to leaving players.