I have heard the expression break off one's plans in the context of breaking off one's holidays due to an emergency.
He had to break off his holidays to come back for the meeting.
What are other examples of its usage?
"Break off" has two meanings that I can think of off the top of my head. The one that you refer to in your question can simply be replaced by "cancel" in all instances.
He broke off our plans <-> He canceled our plans
The second "break off" is a more literal phrase and it implies that something was removed from a greater whole.
"He broke off from the rest of the team." means he left the rest of the team and went off on his own. Likewise, "He accidentally broke off a piece of the vase." means part of the vase was removed from the vase.
"Break" here means:
to dissolve or annul (often followed by off ): So, it's not necessarily followed by "off". It could just be "break."
Other examples include:
He broke off their engagement
They had to break off the dinner partyWe broke off going to the zoo today.
Break off has two meanings:
- 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, 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 (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).