Whenever a task due date it is very logical that asana should prompt to change all the tasks where this particular tasks is blocking it.
Task 1 due date was on Day 1
Task2 due date has a dependency on Task 1
Whenever Task1 due date is extended there is a direct impact on task2 and user should be aware of it.
I have seen this feature in the other project management tool and it works very well.
If in case of delay in Task1 and a user is changing a due date of task 1. Task 2 due date should be prompted to be changed. Currently task 2 likely becomes overdue and one has to analyse and then understand the reason.