Having been thru this stuff, financial/official orgs have policies for accepting a death certificate by fax or mail. If they know your social security number, there is no need to worry a death cert is the ultimate root password to any account. So don't worry about banks / brokerages /insurance etc. Once your SS # shows up on the SSDI list they don't argue much, and that only takes a day or two, or so it seemed.

Utility/subscription type services pretty much get a copy of the certificate and they go away, maybe with a final billing statement. Look out for scammers sending fake invoices to dead people listed in obituaries or legal notice section of the paper.

Where it gets messier is non-financial institution online accounts, but they wouldn't be financially important or time critical. I remember ebay was fairly civil about the whole thing, although I don't remember what they did.