They should use the same method as in Star Conflict: if you combat log, you get locked out of the game for 30 minutes.
I like it. Difficult to see any reason why this wouldn't work, it doesn't intrinsically stop a player from deliberately combat logging but the consequence of doing so isn't so bad that it needs to differentiate between an unplanned disconnect & a deliberate one. It also solves the issue of an aggressor attacking then bailing out - half an hour is easily enough to complete your task in the system & move on.
Perhaps if restricting game access is undesirable a similar rule could be applied to mode switching.