EDIT: Yup, totally misguided here: http://www.physlink.com/Education/AskExperts/ae429.cfm
So, no lunar catastrophe for me (without some other handwavium)
I've read somewhere that the Moon's orbit will eventually degrade (maybe, it's the ocean tides that're causing orbital degradation?).
So, approximately when does this occur? I assume the downward trajectory will happen before the Moon gets close enough to be skimming Earth's rarefied atmosphere.
The only way(s) to stop it would be to speed up the moon's orbital period, or to drag it further out (is that correct?). Or, I guess?, decrease mass's gravitational pull in the Earth/Moon's area (mmm, magic)? Any other options?
When it comes crashing down, it won't be exactly like an asteroid strike - because usually those are coming in at non-trival speeds. However, it's 2,159mi in diameter, and 7.34767309 × 10^22 kilograms in mass - so big boom. But how big? How does that compare to an asteroid strike?