According to a recent study of health insurance policy cancellations, as of December 2014:

Adults with nongroup health insurance coverage reported:

• 91.8% either did not receive a letter about their health plan and any changes that will happen in 2015, or received a letter but it was not a cancellation notice
•  2.2% said their plan was canceled for 2015 because it did not meet new coverage requirements
•  3.4% received a letter saying that their plan was canceled but they did not know why.

Adults with employer sponsored insurance reported:

• 98.1% either did not receive a letter about changes to their plan in 2015, or received a letter but it was not a cancellation notice
• 0.3% received a letter saying that their plan was canceled for 2015 because it didn't meet new coverage requirements
• 0.3% received a letter saying that their plan was canceled, but they did not know why.

Source: "QuickTake: Health Insurance Policy Cancellations Were Uncommon in 2014," Urban Institute Health Policy Center, March 12, 2015, http://hrms.urban.org/quicktakes/Health-Insurance-Policy-Cancellations-Were-Uncommon-in-2014.html