Have YOU in your testament a clause saying: 'And with regard to my art stored in Renderosity, I want that...' ????????

No need. Rosity leaves galleries up when the artist dies.

People usually don't think they would be dead at the next day.

Gebe did not pass away suddenly or unexpectedly. She knew what was coming.

My wife knows what must to do with my PHYSICAL things, but she not at least knows how find Renderosity. Really she don't knows how switch-on my computer neither surfing in the net (because she don't uses it)

Exactly. That is why it's best to make arrangements with a friend who shares your interest, whatever it is. In the case of something like Rosity free stuff, you don't have to put it in your will. Rosity will accept a message posted here to the forums as permission to redistribute if you die. Many have posted such messages.

If I had a store here, I think I would give copies of my products to a trusted friend here at Rosity, along with a letter spelling out what I wanted. I think that would be good enough. I'd probably ask that the products be taken down for a year, then given to a freebie hoster like Planit3D.

Rosity might take all this in mind to create a guidelines or a 'in-case-of-death' form which artists, vendors could sign...

That's an idea, though I don't know what the legal issues would be. It would at least encourage people to think about it.