IO540 asks:
Would ice not eventually disappear if you enter VMC conditions even though it is still below 0C, due to sublimation?
The operative word is eventually. A fair quantity of rime icing can disappear quite quickly once you leave the source of the ice and get into clear air.
By contrast, even a very modest amount of clear ice will often only finally fall off as you push the aircraft into the heated hangar at the end of the flight. This is just a part of what makes it so dangerous.
2D