I know this has been mentioned before, but now that there is a settings section: How about Vacation Mode for when we have to be away from our computer connection for an extended period? I play another browser game; here is how it is implemented there:

Once Vacation Mode is activated, the game is unavailable to the player for the next 48 hours (this is to prevent using Vacation Mode as a defensive tactic).

Vacation Mode auto-expires at the end of 30 days (it can be turned back on, but this requires accessing the game again).

(Translated to Galaxy Legion - While in Vacation Mode)
1. the player's ship will not require upkeep and will not appear on anyone's battle tab.
2. the player's planets cannot be invaded (they could still be scanned)
3. the player will not contribute to the legion bonus (but will have a special icon differentiate them from an inactive player for the situational awareness of the rest of the legion).
4. all planetary production ceases.

edited to add:

Not sure if it might be nearly impossible to block access to a game played exclusively through FB (without blocking out FB), so, maybe this could be activated with some sort of newly minted artifact?

"Suspended Animation Pod" allows the player to activate Vacation Mode from their Settings section. If the artifacts aren't available in an artifact haul, but maybe from an NPC, that would help keep Vacation Mode from being overused (or used too much as a tactic).