Whether they sell or not is irrelevant. Folks who bought in 2001 (or even 2002 for that matter) or before with decent mortgage terms and no equity extraction can easily rent their property out for positive cash flow (at least in the central SD areas I follow).
For the moment.
When all those empty houses are back on the market post-capitulation it will drive rents down along with everything else. Landlords will be competing as much with cheap houses as each other (and high unemployment).