So the laptop from your OP was never dead in the first place?
That is correct. I oversimplified the situation, thinking “I just need to know whether or not I can get the files off by mounting it externally”. In reality, the laptop is not dead, the laptop’s owner is. His surviving spouse would ideally like to get any personal files off of it, as he didn’t leave a will and she’s finding it complicated to identify his assets and move towards setting his affairs and cancelling any auto-pay arrangements etc etc.
If the spouse can find old printouts of tax records, they may help figure out the accounts. The tax filings will have forms from accounts which had income associated with it, like interest or dividends. If you used a tax service, they will have those records. Once she has been officially designated as the executor by the probate court, she should be able to gain access to his bank accounts. The bank account history should have records of auto payments and she can contact those companies as executor to gain access to those accounts.
This kind of situation is one reason why I don’t like going paperless for everything. When statements come in the mail, the executor can can figure out the accounts of the decedent by looking at what comes in the mailbox. But when everything goes to the decedent’s email, the executor may have no idea what accounts they had.