Your response deserves a whole book, but I will give it only one post. The assets did vanish. A house is an asset to a lender only because it has value. If it remains in place, but ceases to have value ... you are telling me that it remains an asset to a lender?
The assets remained. Their perceived value changed.
If you have a home valued at X, and a change in the market reduces it's sale price to 80% of X, have you lost your asset?
Mortgage backed securities have a monetary value at the market. Absent that, they are ink on paper, or mere electronic signals. If the monetary value vanishes, the "asset" is still there?
The mortgage is still there. If the buyer is still paying it and continues to pay it, it has just as much value to the investor as it would have otherwise. People who buy these are looking for long-term investments.
In my real world example, OneWest bank made off very well because they were able to buy the assets (mortgage debts, if you need cliff's notes) of IndyMac at a time when the perceived value of those assets were very low. As this scandal unfolded, it was revealed that the underwriting, which is the work done to consider the assets and credit worthiness of the borrower, often inflated the value of the property and over-stated the reliability of the borrower. For a period of time the value of these tranches of mortgage backed securities was unknown and unknowable. That's what destabilized IndyMac.
OneWest had the foresight (well, liquid assets really) to look at those tranches of mortgage backed securities and realize that:
1) Most of them will be paid as agreed.
2) Many of the ones that aren't will be refinanced and paid off anyway.
3) Even where the borrower completely defaults, the loan is still backed by property.
4) Heck, if we can buy this pile of manure at well below market price we can even tinker with the terms of the loans to recover most of the value while minimizing foreclosures which have the side effect of further reducing property values in that neighborhood.
Now one can hold on to them in the hope that the "asset" might reappear, which is what I presume you mean, putting the best construction possible on your words. However the asset as understood by the agency that lends against it is the value at the market. If that vanishes the asset has vanished. It may recover, but that is extremely doubtful in the case of the "leveraged" assets typical of the 2003-2008 bubble. As it was in the case of the common stock bubble that ended in 1929.
Nonsense.
If you have a mortgage and I hold your mortgage, that asset doesn't vanish just because market conditions lower the value of your home. You still have a mortgage and you still make the payments, and I still have an asset which is a lot like a 30 year annuity.
Worst case scenario for me is if you're upside down in your home, meaning you owe more on it that it would sell for, and you decide you will come out ahead if you just walk away and leave me with the house. In that scenario, I basically have the asset of being the mortgage holder forcibly exchanged for having the asset of the home. Do I lose? Yes, but my loss isn't anywhere near 100%, more like 20%-30%.
Now if you've wrapped your head around that, just imagine that I actually owned ten of those mortgages and only one of them defaulted. That cuts my losses
from the initial market evaluation from 20%-30% to just 2%-3%.
Then if you've wrapped your head around
that, understand that it represents a default rate of 10%, which is huge. More realistic default rates for high risk mortgages are closer to 4%. For regular mortgages, much less.