I just end up rewriting/tweaking them as I go. Frankly, sometimes a single spell changes the rotation timings so much that there's just no easy way to add in a step and be done with it.

That said, if you just want to cast things in sequence regardless of whether a single spell fails or e.g. is on cooldown, etc., just add them to a series of steps. A mapped key step failing will not block like a castsequence spell failing. The caveat is that you can't easily put things in a direct sequence in steps without using the somewhat arbitrary "do not progress to next step for x.x seconds."

A lot of people use the Gnome Sequencer addon to control everything as it "works around" spell failures. I keep waiting for that addon to get PNG'd but so far it's still available.