Over the course of a given rental, unless the property was purchased almost immediately before a real-estate crash or rental crisis, the amount of cashflow generated by a tenant will cover the majority of the volume required to generate equity in the property.
In certain cases, the financing for commercial real estate, for instance, will literally substitute the credit rating of tenants for those of the landlords - because ultimately that's where the money is coming from.
If a landlord is rendered insolvent, they aren't even rendered destitute; they sell or refinance the property to generate liquidity. If many landlords do the same thing, the volume of real estate on the market increases, the price of real estate drops, and the market is now on it's way to pricing in the effects of the shock which caused the crunch.
The fact that we've been spewing money at asset holders for over a decade is why real-estate metrics are so out of line from historical cycles.