No, even if you logout from your device your cards will be visible to you once you log back on. However, if another user logs into your device then Paytm asks the new user to delete all the existing activated cards before the new user can activated a card of their own. In such a scenario if the new-logged user chooses to delete your cards then activated cards will be deleted from the device. Also, if you uninstall the Paytm app your activated cards on the device will be lost.