You can maintain a waterfall-style project plan and use that to feed stories into your agile sprints. If something needs to change, then you feed that back up i

You can maintain a waterfall-style project plan and use that to feed stories into your agile sprints. If something needs to change, then you feed that back up into your master plan, just like you would if you missed a milestone. The difference is that, with agile, you get more continuous feedback and you explicitly model iteration in your plan (since if you're doing it right, you're delivering progressively more capable versions of the entire system and not just components to be integrated at the end). Nothing in agile precludes long-range planning, or taking deadlines into account.