Well, it's been some time since my last failure, though depending on how you count it my catching up post probably qualifies as a de facto failpost. Back then I concluded that I would keep writing posts as normal even if I fell behind, and separately fill any missed posts with (avian) content. In theory this should mean that my posting system has positive stability: it gets easier to catch up when I'm behind.
There have been two issues with this, though. The first is that some of the bird drawings have been surprisingly difficult. Some, like the Philippine eagle or Major Mitchell's Cockatoo took much more time than the equivalent bit of writing would have. A lot of this is just that I get carried away with whatever I'm drawing. But even if I didn't, generating extra content is still hard. Worse still, if I fall behind it's often because of external disruptions or drains on my time that mean I don't tend to have the spare capacity to fix it.
The other issue is that I've stopped doing failure posts because I've had birds to fall back on. This is a problem partly because failposts are easier than birdposts as per above, but also because failure posts were serving an important function as a way to recognise that failure, call it out, reflect on what caused it and how to stop it happening again. Without doing that it's easy to have failures happen casually, and even lose their significance. I probably would have reflected on the effort of the birdposts sooner if I'd been doing failure posts as well.
I'm not sure why I stopped doing failposts, maybe because birdposts let me dodge having to call it a failure, but it seems like a mistake and one that's easy to fix. From now on, a single missed posts merits a failure post, and multiple missed posts get a failure post plus whatever extra posts I need to catch up. That's still either birdposts or any other content I can think of, but I might give some particular thought to other kinds of content that might be less effort in a pinch. It could be that the answer is to find some way to piggyback off other things I'd be doing anyway.