As far as I know, by default, you are not logged automatically out of the Webex Mobile app, except if the admin has:
- set up your account to be deactivated after a period of inactivity. In which case you won't be able to use your Webex account on any platform (not only mobile) until reactivated.
- set up the single sign on option to force you to log in again after a certain amount of days.