The description sounds similar to an incident on a 1900 about a year ago. The pitot heat weren't working and froze and the crew lost all air-data and orientation in IMC. Thankfully broke cloud at about 10 000' and landed safely.
Only difference is the 1900 has pitot/static ports and the King Air has the static ports at the back. The King Air 200 also doesnt have a pitot heat warning.