I want to access a deceased user's Heroku account.
If the deceased user's account has a company email domain, you can follow the same procedure outlined in our help article titled What should I do if the application owner has left the company and I need to transfer ownership? to resolve this. Basically, you can ask your company IT admins for access to the deceased user's company email address. If the email address no longer exists, you can ask them to reinstate it - you could then simply reset the password for their Heroku account.
Otherwise, the person/entity requesting access to the deceased user's account will need a court order that names the requestor as the rightful inheritor of the account/application and the deceased's personal information. This must specifically sufficiently identify the account at issue (by username, account number) and order that we transfer the account to the respective individual.