Apologies to @apm for the tongue in cheek title, but let's talk a little more about the perceived commitment of social media, resulting in the sense of needing to announce our exits.
I've posted a few "Goodbye" posts over the years on social platforms, but they were primarily on forums or mailing lists where either I wouldn't get notified of posts directed at me (forums), or I was unsubscribing, and would no longer be receiving the messages (mailing lists).
I've never felt the same compunction on the current batch of planet class social platforms. Chances are, I will get notification of the activity via a push notification or email, and these days, I tend to drop a profile on platforms whether or not I intend on using them for the long run, just to have a login there should I choose to use it.
Cake is one of the first platforms to really benefit from that behavior. I had a burst of activity when first testing the platform, noted the current low level activity, and only came here when I thought I had something thoughtful to share (given that thoughtful posts tend to do better to spawn thoughtful conversations on smaller platforms than on large).
However, given that I'm married to my inbox, every time a tag or reply or reaction came up (like APM's on their exit post), it was an excuse to take a break from what I was doing and pop over.
When more notifications come through, I'm here more. When less come through, I'm here less. Nowhere in that range does the thought "Delete my account" come up. As @Chris mentioned in his comment on that thread, I have lots of platforms like Quora where maybe I participate, maybe I don't.
The one place where I do see "Goodbye" posts frequently is Facebook Groups, where you leave a trail of greyed out name posts behind, so it seems appropriate to say something if you care about folks in the community.
For Cake, though? Leave your account live, @apm. The worst that happens is you're reminded of or drawn into a thoughtful conversation.