Squill ~ Good question.
"Without notification" is to not let TIFFS know you're no longer a part; ergo, you're still open to attack.
Notification, I think, is necessary.
A member who is not currently involved in a conflict should be able to leave immediately.
But is the person in question joining to launch an attack then immediately quit to the safety of GC?
The next question is what are the rules of re-joining?
Should continuously weakened players allow a person to quit, strengthen up then rejoin with a massive fighting force? Hell, no.
Maybe a TIFFS council vote would be in order; but then, how would a TIFFS council be operated?
Maybe the current inhabitants of that player's region should vote on it.
If that person has grown significantly while out of TIFFS -- and intends to bring those resources to benefit the inhabitants of that region -- then maybe the inhabitants of surrounding regions should be the ones to decide.
This is a tough decision to make but I definitely think the circumstances of the moment should be weighed if / when the situation arrives.
P.S.
Please remember that I'm not claiming dictatorship over TIFFS. All rules should be suggested, formed and agreed upon by persons who are interested in taking part.
Any suggestions?