Retain flexibility with habits?

I don't know of a specific technique or anything simple to recommend, but I think I can say something useful nonetheless.

I think there's a way schedules can loom large in human minds, shaping our experience of reality where we feel ourselves to be within the schedule, routine, or whatever you want to call it. It comes to feel familiar and we have expectations around what will happen now and next and that shapes our perception of each moment when we believe ourselves to be held by the schedule.

Of course, the schedule doesn't really exist; it's a construct that exists only to the extent we believe in it, and therein lies the trick. Whether or not you feel flexible or if you feel like you've given up depends on your relationship to your expectations for what is going to happen. You can pay attention to the way this relationship forms in your mind, changes under different circumstances, and use that as a jumping off point for freeing yourself from feeling one way or another because you slept in or are keeping your routine.

I wouldn't recommend trying to avoid giving up or anything like that, though. Rather, I'd suggest just noticing what happens when you keep or don't keep the schedule and let yourself evolve things from there without trying to force the situation. There's as much to learn from the feeling of giving up as there is from the feeling of flow, productivity, or success if you pay attention to it.

G. Gordon Worley's answer is much more profound and perhaps more powerful but sounds like it could take some time to come to fruition. In the meantime: how about creating backup plans for the most common failure modes? For example, if I wake up late, then I will...

I'm still not great at this myself, but I find it sometimes helps to add fixed points throughout the day, ideally ones that involve obligations to other people. Like "No matter what, I'm feeding my pets at 8:30, walking the dog at noon, talking to my boss at 3 about the project I am scheduled to work on in the morning, and sending that email to a client by 5pm." Right now I have a system where at the end of the day, before 5pm, I send my boss a quick note with a list of my projects and their status. He doesn't really care how much I've gotten done on any given day as long as it averages out, but it's helpful for him to know, and it's enough of a psychological nudge to help me get back to work and focus throughout the day. Usually.

My other "solution" is very short term, but I find my ability to focus goes way up if I'm so overscheduled and approaching deadlines that the things I need to do push everything else out of my brain. Of course, that's not a great way to live, and prone to backfiring in many ways.