treating insurance premiums as qualified medical expenses..

No, the health care continuation coverage is referring to health care whose premiums you have to pay out of pocket with after tax dollars. No employer-subsidized health care premiums will qualify for this.

The law specifically refers to "a health plan during any period of continuation coverage required under any Federal law" - which includes COBRA - "A federal law that may allow you to temporarily keep health coverage after your employment ends, you lose coverage as a dependent of the covered employee, or another qualifying event. If you elect COBRA (Consolidated Omnibus Budget Reconciliation Act) coverage, you pay 100% of the premiums, including the share the employer used to pay, plus a small administrative fee."

To my knowledge (but I am a tax professional, not a labor professional), there is no federal law that covers the insurance needs of people who voluntarily retire early.

P.S., another reason to be able to pay for health insurance premiums from your HSA would be when you are paying for "a health plan during a period in which the individual is receiving unemployment compensation under any Federal or State law"...however, I assume that a retired state employee would not qualify for unemployment - but, then again, I am not an unemployment expert, either.