The IRS ruled that former employees (I posted the link in the retirement forum a few weeks ago) who are eligible for COBRA and retiree insurance but choose not to enroll are eligible for insurance and subsidies on the exchange.
an individual will not be eligible for retiree coverage unless the individual enrolls. Therefore, an individual who is eligible for retiree coverage but does not enroll disregards that eligibility in determining qualification for the lack of affordable coverage exemption. source
Running out of benefits however doesn't count as a qualifying life event and a person would have to wait until open enrollment on the exchanges to switch to a policy with no lifetime limits.