This is the 16454th most frequent Russian word.
рухнули
"Rухнули" means "collapsed" or "fell down."
Here 'рухнули' is used in its literal sense to describe the physical collapsing of structures.
Во время землетрясения стены здания рухнули.
During the earthquake, the walls of the building collapsed.
In this sentence, 'рухнули' is employed metaphorically to express the emotional impact of loss or failure.
После потери работы все его мечты рухнули.
After losing his job, all his dreams crumbled.
Here 'рухнули' is again used metaphorically to convey that an expectation or intention did not materialize as planned.