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:
Other examples include:
Break off has two meanings:
Your example, break off one's plans, is the first meaning.
Browsing COCA, we can find plenty of examples:
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).