I thought I had a rep but it seems I didn't save it :(
You need to prepare yourself for any type of harass that other players can use against you given the map. For example, on Xel'Naga Caverns you always have the risk of P or T harassing your mineral line at your 3rd expansion from the cliffs.
With that being said, you need to prepare ahead of time to counter that possibility. You already done that by going for the quick muta but what else can you do? You can place an overlord outside of his main and sacrifice the overlord to get as much intel as possible. If you see a factory with a tech lab and a starport you can tell yourself, "Ok there's the possibility of him dropping the cliff at my nat, what can I do to delay it?". Be aggressive at his choke. Place overlords between the cliff at your natural and his main so you can see when the medivac is beginning to move out. Place a spine crawler at the edge of natural just to DELAY the push until you get your muta's out.
And if you see that your natural is nowhere to be saved, abandon it, dont waste units, pull back, and expand somewhere else. More than likely, I always see a Terran expand behind that cliff drop. IF he does, you should be safe expanding somewhere else.