KiNgBrAdLeY7: When its owner dies, or is unable to access it themselves completely for whatever reason?
Also, is transferring it to somebody else possible, like other possessions of material value? Possible like clean, legit, as being "allowed to", or just confiding your login info, email, credentials to somebody else and instructing them to not reveal the change of ownership?
If the owner dies - and I've been through this, sadly - you contact support. They will tell you what legal documents they need from you. If you provide those, they'll grant you access to the deceased's account. Means, if you are entitled, you'll "inherit" the account. Transferring or merging to another existing account seems not to be possible.
When I was in the situation, I didn't went through with it, because the person who died had mostly the same games as me, and also it would have been too painful to sign in as him... although I could have provided all the necessary paperwork.
What I can say is that support was extremely forthcoming and empathetic - it was one of the darkest times in my life and this was one of the upsides and one big reason I still feel some loyalty to the site, although a lot of things have gone downhill sadly in the last few years (for which I blame management, not the grunts at the customer or coding fronts).
Support - overloaded and overworked as they are now with the botched CP2077 release, the CDPR hack and buckloads of new releases - has always been a forte of GOG. Back then, even emotional support, which was awesome.