The phrase "fall to bits/pieces" can be used to describe something that has completely broken or fallen apart. Some synonyms for this phrase include "crumble," "disintegrate," "dissolve," and "break down." Other possible ways to describe a similar situation could be to say that something has "fallen apart," "collapsed," or "failed." These terms can be used to describe physical objects, but can also be applied to more abstract situations, such as relationships or plans. Regardless of the context, these synonyms all capture the sense of something falling apart or failing to hold together.