At the risk of possibly sounding crass, the practical solution is to simply never tell them of the decedent's passing.
Unless the matter of concern is a legal or financial one (eg: bank accounts, pensions, insurance, etc.), quite literally nothing and nobody else requires knowledge that the account holder passed away.
Never tell Valve that your gamer dad passed away and they will be none the wiser and noone will have any problems as you "inherit" his account and its associated games. You're not trying to defraud Social Security as a 150 year old, after all (...right?).
This might work for the first generation of steam users for now, but eventually they might require some kind of verification for old Steam accounts. Also remember that Steam is providing two things - a license for the games and a service to download them. I wouldn't expect a court to agree that a relatively low one-time fee obliges Steam to provide your or your heirs a service in perpetuity.
Why take the chance for games that you can get DRM-free and transfer independently from some live service.
Unless the matter of concern is a legal or financial one (eg: bank accounts, pensions, insurance, etc.), quite literally nothing and nobody else requires knowledge that the account holder passed away.
Never tell Valve that your gamer dad passed away and they will be none the wiser and noone will have any problems as you "inherit" his account and its associated games. You're not trying to defraud Social Security as a 150 year old, after all (...right?).