A. Invest your HSA savings is much better than spending it, here is why.
HSA is a great way to save for your retirement, because the HSA savings are not taxed on the contribution going into your account, not taxed on the investment earnings, and not taxed on the amount withdrawn from your account when you retire and pay for medical bills or Medicare premiums.
Remember, you need to pay for Medicare Part B anyway (currently at $115.40 per month per person), add $30 a month or more if you buy a Medicare Part D prescription drug plan.
Compare HSA with traditional IRA or 401(k), the later two options only allow you to have deferred growth until you retire, while HSA is entirely tax-free!
You can leave your HSA contribution remain invested, and you are typically presented with an array of investment options, just like your 401(k) plan's choices. And your HSA investment strategy should be similar to your 401(k) investment strategy, since they have the same time horizon.
Of course, the above recommendation is based on the assumption that you do have some spare money to pay for your current medical expenses.