Luckily, I work in an industry where you are expected to work very hard, but, in general, vacation time is respected. However, due to various filing deadlines imposed by the IRS, SEC, bank covenants, etc. people do look at their client load in order to determine a reasonable time to take off. There are period of the year where week long vacations may not be allowed.
That being said, if an unforeseen situation arose that made someone cancel their vacation, the firm would help reimburse any sunk costs. Bosses and managers are not on power trips and ask people to cancel vacations on a whim and in general, they try to work with you on your timing..