Well, sure, but if you're doing the "The 1 side project per month challenge" and the "1 side project per month" part is optional, what are you actually doing?
Obviously the "1 side project per month" part is not optional, it's conditional, which is something different.
The "1 side project per month" challenge being conditional on not having too much success with one of the monthly projects (thus prompting you to stop and focus on that) is not that different on it being conditional on numerous other things:
1) In that you continue to want to do the challenge (e.g. it's perfectly legitimate to decide it's BS and give up after a few months).
2) In that you have the time to do it (e.g. you might suddenly have to stop because you have too much on your plate from your day job a few months in).
3) In that you are able to do it (e.g. you might have to stop if you have a health issue).
And tons of other things besides.
So the question makes no more sense than asking "if you decide to run at your local marathon, and you stop after 12 miles because you got tired, or because there's an emergency at your home, or because you strained your ankle, or because you just felt like it, then what are you actually doing"?
The answer is obvious: you are doing the challenge for AS LONG AS YOU PLEASE.
