Since your husband is on Medicare, he can no longer contribute to his HSA.
On the other hand, he can still spend money from the HSA on qualified medical expenses with the tax-free dollars in the HSA until the HSA funds are exhausted.
Unfortunately, you don't get tax benefits just from having an HSA, it's from making tax-free contributions to the HSA and then not paying tax when you pull the money out for qualified medical expenses. He took the tax benefits years ago when he contributed to the HSA.
Note that once he turns 65, he can treat the HSA like an IRA. That is, he can take money out for any reason, so long as he pays income tax on the distribution (just like an IRA). There is no penalty in this case.
