depends on how the real estate price is determined. If banks hold the properties they only have a liquidity problems; if they sell the properties (at the current marketable price) then they have a solvency problem.
In overall bank deposits it is hard to estimate the losses. But in mortgages I have a better idea. We are in the process of closing on a HUD condo (1 bed 1 bath) for my daughter. The condo is only 9 years old. I was able to find the original new list price which $79,900. These were probably in the 5% down payment range leaving $75,000 on the mortgage. We got it for $9,250 (not bragging to hurt anyone) leaving $65,800 or about an 87.7% loss. I would have to assume banks are in the same category. This property is not typical though (too small for a family). In looking at the HUD single family homes the losses appear to be about 55%. When I put them together I get a very rough figure of about 61% in losses. So banks with large loan portfolios say 50% could have 30 % of their portfolio taking this kind of loss. Putting it together I get 15% of the bank with 61% losses or about a 9% loss in capitalization. This is a SWAG but when taken with these monster trillion dollar banks we are looking at 90 billion per trillion. Translating this to deposits is tricky because of the reserves. My guess is in the 15 -18% range. This one is tough to do the arithmetic on. I probably have missed some factor. With uncle ben and the FDIC picking up the tab its going to be a mess for years to come.