No, alerts will not disappear automatically upon an account's behavior changing.
Alert functions as a timely notification/task upon customer behaviors you define. The idea is that you get an alert/alert task and you should take action right away to resolve the situation and close the alert task, or if no action is needed, you dismiss the alert.
Once triggered, an alert or alert task will remain open until you close/dismiss/delete it manually. Natero does not auto-delete an alert upon the associated customer behavior changing as that's contrary to the primary purpose of an alert - timely notification and call to action.
If an alert is not set to never-retrigger, you need to proactively close/delete/dismiss an alert or alert task in order to receive a more up-to-date alert upon the same behavior for the same account.