can an account holder bequeath her/his digital game collection (e.g. GOG.com)?

If you gave someone your log in information, I suppose they could log into your account and download the games you've purchased onto their machine.

It's almost certainly not allowed by the TOS/licence agreement, but I see nothing morally wrong. Really though, there's nothing stopping you including your email address and password in your will. :P

The EULA prohibits transfer of ownership. Your copyright act permits transfer of ownership. The rights holders should not be awarded damages for copyright infringement but you could possibly be held accountable for breach of contract.

That's really the one flaw in digital distribution; the lack of an ability to re-sell/transfer your collection, in part or as a whole. I'd like to say that is something that will eventually be legitimately corrected (as opposed to the questionably legal workarounds proposed here), but I seriously doubt the publishers will allow that to happen. They already don't like that they don't get a piece of physical used game sales (which they shouldn't); with digital distribution, they are completely in control of that aspect of game sales, so I don't see them giving that up anytime soon.