The plan will break. Your ability to adapt is the real plan.

Every plan is built on assumptions about a future that has not arrived, so breaking is the normal outcome rather than proof you planned badly. What separates people is the gap between the plan failing and them noticing they need a new one. Some spend weeks defending a schedule that stopped matching reality. Others adjust within a day and keep the goal.

Decide in advance what you would do if the main route closed, even roughly. Set a checkpoint where you look honestly at whether it is still working. Changing the route is not the same as abandoning where you were going.