I regularly remind myself that the only requirement for membership in AA is the desire to stop drinking. This means that as long as I am not drinking, I can always return to meetings if I feel I need them. I've cycled in and out of the AA program, and the most important thing for me is to know at my core that my involvement with AA and my commitment to sobriety are two different things.
I would consider just letting your sponsor know that you're breaking off contact (although I understand wanting to avoid the "institutions, jails, and death" outcome monologue)...if there is any way to send a card or a note that simply says "thank you" for the time and energy you've put into supporting my recovery, I plan to stay sober, but am involved with a different recovery program, etc. it might help you feel that the door was left ajar - both in case you ever wanted to return and so that if you run into ex-sponsor in the supermarket you don't have to feel awkward...
Our sobriety is fully our own journey, and we will pass through many cities and meet many helpful strangers on the way. I see it that way, and count AA characters who have crossed my path as many of those "helpful strangers."
I'm way pulled back from the program at the moment, though powerfully and fully sober. I too feel immediately furtive and sketchy as soon as I stop attending meetings, and then notice that feeling rise up inside me and dismiss it. Guilt is not the right reason to include meetings in my life. I have many activities which support my sobriety, and as I cycle in and out of them, I don't have guilt about that - only AA. It is definitely an aspect of the teachings of the program, there is some fear bred there - intentionally - and when I recognize it I have to re-affirm for myself that I don't accept that fear into my own sobriety. I do not think that choosing to not attend meetings destines me for the gutter. I believe my decision to be sober stands alone, and that all the methods and supports I collage together toward that purpose are tools applied to the sculpting of my sober life. My life is not the tool, and the loss of one or even a few of those tools does not prevent me from continuing my creative masterpiece, my obra (greatest work)...