You will be removed from the alliance due to inactivity according to the following rules:
0 to 5 000 points : After 14 days of inactivity
5001 to 10 000 points : After 21 days of inactivity
10 001 to 30 000 points : After 33 days of inactivity
More than 30 000 points : After 180 days of inactivity
The system will remove your account from the alliance at the end of the time so that your fellow players can capture your base stations. This is independent of your platinium level.
So you can also go on holiday for a longer time, depending on the situation. If the holiday should last longer than your deadline, you can log in via mobile phone and the time starts again.