I would go in as other's suggested and explain the situation. You asked about this time off well in advance. There was a meeting where such and such was stated. You booked your arrangements upon this information.
At this time, you cannot change your travel arrangements due to financially losing funds.
Will the time off be approved or will this count against you?
As others stated, be prepared to hand in your resgination. But, I would also be prepared to leave at the end of that day or after talking with said boss. If this boss is as you describe, I can only imagine what will happen when you do give notice.
And honestly, if this company is like that, if the job market was good, I would probably not say a word, but the Friday before my vacay, pack up my desk at quitting time and let my resignation letter on my boss' desk. That is what I would do in my head, not so much in real life.