What it is
An HSA needs a qualifying high-deductible health plan. Contributions reduce taxable pay, growth is untaxed, and qualified medical withdrawals are untaxed. The account is yours, not the employer plan, so it moves with you; employer-funded balances follow the account agreement.
What to do about it: Keep the receipts for reimbursement after you leave. An employer contribution that was promised in writing can be claimed on the final settlement like any other earned wage.
Plain-language description of US practice, not legal, tax, or financial advice. The paired guide carries the citations, dates, and thresholds; the state pages carry the local windows.