Capt Claret,
I don't know if I'm unlucky, but I have had 2 pitot heat failures, both worked during pre-flight, and broke sometime between when i next turned it on and when they was full of ice and airspeed (indicated) was decaying quite rapidly(an alarming site).
Luckily this particular aircraft had to pitot systems and 2 ASI, so I used the co-pilot's side for the remainder of the flight. The other one was in an older [read normal GA age] piston twin. This one didn't have 2 ASI's, so just had to use standard rates of descent and normal descent power settings to get back down below freezing safely. Not much fun.
Basically in turbo-props I have flown, as soon as you hit IMC, eyes flick to OAT gauge, if less than 10, all engine/prop anti-ice goes on, and pitot heat (that is just my method). Then you just keep an eye on the wings until you need to make the leading edge go bumpy to get rid of that ice!