HSA is yours to keep forever. I recommend using Fidelity, no fee and access to all the best investment options. You should transfer all funds from an employer sponsored HSA if it's not Fidelity to Fidelity.

Any medical expenses you incur while you have a qualifying high deductible health plan (HDHP) can be expensed anytime in the future from your HSA. What I do is invest all of the HSA funds, and pay for all of the medical expenses with after tax money. I pdf all of the receipts for the medical expenses, and now, if ever in the future I need cash, I can withdraw it from the HSA penalty free since I have proof of the medical expenses. If you don't end up having medical expenses (good luck), and you turn 65, then you can withdraw and pay regular income tax like an IRA/401k (if you need the cash, you should of course use up your IRA/401k first).

I don't even understand how the government plans to prevent fraud if people decide to claim the same health expense multiple times, as you only have to keep tax records for a few years, and the law as it currently is lets you deduct health expenses from anytime in the past at any point in the future.