Theres is sometimes a reason why a captain cant be there.
If a player did not log in for lets say 2-3 weeks, you can kick him out
The captain just had to be present once in the next 15 days.
I don't understand why he couldn't be active or at least send a message to other team mates for 3 weeks.

Thats why I did suggest earlier that people can see when a player did log in the last time.
That's useful too but if you see that your captain was active before 10 days and he isn't active anymore (dropped by will or force), it can't help the situation.