Microsoft Project Professional 2010 enables you to cancel a task but keep a record of the task in the project plan. This is called inactivating the task. The task remains in the project plan, but does not affect resource availability, the project schedule, or how other tasks are scheduled.
When using automated scheduling it does affect planning.
Task 5 jumps to the the earlies date possible (today) and does not see task 3.
Conclusion – simply inactivating tasks brakes the task dependency.
This is the prefferable solution because it does not add any constraints to automated scheduling, the project can be rescheduled as earlier as later.
Make task 5 dependent on task 3
Start No Earlier Than
This solution adds a new constraint to the project planning and thus makes it more complex to follow.