So what happens when the real estate market tanks like it did in the years 2008-2010? Would the government eliminate the liens it put on your house since now it

So what happens when the real estate market tanks like it did in the years 2008-2010? Would the government eliminate the liens it put on your house since now it's not worth as much? Or would this work like stock options where they tax you on a paper gain even though you haven't sold the house so you risk ending up under water?