Assume that the Blue Moon clone takes 2 weeks before its ready to bottle, and will also net you 42 bottles.
You have 24 empties on hand. That means you need to have 42 - 24 = 18 additional empty bottles in 2 weeks time.
If you can drink 18 bottles of beer in 2 weeks, then brew it. Even if you can't drink that much, brew it anyway. The Blue Moon can sit in its carboy until you are ready to bottle.
Either way, logic implies that you must brew.