In order to transform the way our society regulates marriage, there would necessarily have to be some transitional regulations.
For the purposes of Social Security survivor's benefits, a non-working spouse should be considered to have contributed because the tax withholdings came out of the shared pay-check. So, in answer to your questions, in as much as the non-working widow had a shared property relationship with her deceased husband, she should collect on his Social Security survivor's benefit.
Under the non-marital regulation, if people wanted to have community property, they could make such a binding agreement, and it could work the same way. This is a detail that would have to be worked out, but there is no reason it could not be worked out that way.