Well. I imagine it was just a partial collapse. Let's say that merely the ceiling of the Oval Office caves in on Truman, and he is able to get out without serious injury. Several chimneys, ornamental bits and possibly that curved veranda collapse as well. The renovation immediately takes place, of course, but in this case it seems to me that there would be calls for immediate structural reports on all major landmarks (particularly pre-1850s) and perhaps the organisations about protected/protecting buildings get a boost.