[Break off][1] has two meanings:

>  1.  To end abruptly, either temporarily or permanently. 
 2. To remove a piece from a whole by breaking or snapping.

Your example, *break off one's plans*, is the first meaning. 

Browsing [COCA](https://www.english-corpora.org/coca/?c=coca&q=11533527), we can find plenty of examples:

> What caused you to break off the last engagement?  
> Break off communication with the Earth shuttle at once.  
> ... prompting him to break off relations with his Venetian publisher in 1730.  
>... demanded that their leaders break off the negotiations.

[Break][2] (definitions 6, 7, 8 in OALD) can be used without *off* in a similar sense, meaning to "end something" by interruption, forceful action (as if snapping), or by severing a connection. For example, you can *break someone's fall*, *break a fast*, *break a tie* (to determine a winner) or *break all ties* (to stop talking to someone).


  [1]: http://en.wiktionary.org/wiki/break_off
  [2]: http://www.oxfordadvancedlearnersdictionary.com/dictionary/break