Because a meet me conference is not an ad-hoc conference, the call will not go point to point when only 2 parties are left and it will not drop with only one party left. These are both ad-hoc conference feature. The only way to end the external caller's call is for them to hang up. If that disconnect is never received, then the call will stay up until the max call timer is reached. The only way to end that call automatically is to drop the max call active timer. This parameter is set on a system wide basis, so the numbers should take into account the max time you expect any one user to be on a call. If you set the number to 120, then any single call in the system that has been active for 2 hours will be dropped without warning.