As you were.
Once I cleaned up the board and had a good look with m' trusty folding magnifier under decent light and poked it with m' DVOM it turned out that the soot all over the mic5219 wasn’t from the mic5219, but from an adjacent pcbtrack that looks to have been bridged using solder which for some reason vaporized, leaving an open circuit. When bridged using a bit o' wire with a portable 3v supply connected to the power socket, the power LED burst into life again so it looks like a relatively simple repair. Still don’t know why whatever it was blew in the first place.
It looks like the track was open circuit at some point and had been repaired with a solder bridge, and the repair blew out. Should be an easy fix, like I say. Onward and upward.