Starcraft – Does Blinding Cloud not affect Widow Mines

Glaive-worms will only bounce to visible targets. If you don't have some way to detect the burrowed enemy, your mutalisks won't randomly hit them.

Burrowed Units take splash damage, the same as if they weren't burrowed.

Start splitting your workers to your other bases, if you have any, and they aren't already saturated. You mentioned you waited for energy to scan, It'd probably be quicker/easier to get one or two of your mineral workers to throw down a couple of missile turrets (out of reach of the mines) as soon as you figure out what's going on, as opposed to waiting for your scan to refill.

However preempting this sort of attack is probably the best strategy. A drop is a fairly common tactic, but can be easily thwarted or even deterred entirely by a fairly thin defensive line. drop One Missile Turret (Terran), Photon Cannon (Protoss) or Spore Crawler (Zerg) and they would have provided enough detection for your other units to quickly clean this up, and would act as a deterrent for the initial drop as well.