Most loss of coverage will be because people CHOOSE not to buy insurance.
https://www.cbo.gov/sites/default/files/115th-congress-2017-2018/costestimate/americanhealthcareact.pdf
CBO and JCT estimate that, in 2018, 14 million more people would be uninsured under the legislation than under current law. Most of that increase would stem from repealing the penalties associated with the individual mandate. Some of those people would choose not to have insurance because they chose to be covered by insurance under current law only to avoid paying the penalties, and some people would forgo insurance in response to higher premiums.