There is no way a Hotel is going to pass on a "Large Group. I don't know if the large group is 50% or 100% of the hotel the night before! Anyway no hotel is going to pass up on that money. I am sure they will compensate you! Even if it is free food and drinks that outweighs probably how much money they are making. I would be satisfied getting bonus points and free food and beverage.
I will say this though. If I had a dinner to get to at 6pm and was flying in expecting to shower and change when I arrived at 4 but now can't I would be little upset!