That boss was a short-sighted moron. (I assume we all can see that). I hope that role is as high up the food chain as the Peter Principal will allow them to go.

1). Hiring is expensive, scouting, ads, interviews, and paying HR do process their onboarding and benifits. The rule of thumb Ive see previous managers use is the total cost to hire someone is 2-2.5 times their annual take-home. Not to mention the effectivness of a new hire learning the role costs the company real resources, time and effort to bring up to speed.

2). Your PTO is part of your compensation, and can be used within policy as you see fit. Failure to allow its appropriate use could be viewed as wage theft and there are very powerful leagl avenues (depending on location) to take if the case is big enough to bring against the employeer.