One workaround would be:
- put a task before the task you want to make disappear, and put on it a dependency on the alternatives.
- set "complete in oder" on the master task.
- as long as the dependency is not completed, the "previous" task will not be active, and the desired task will therefore be active.
- when completed, the first task will be active, and therefor, the second on will have to wait.
( the "first" task migh be named something like "delete next task").
Olivier