Brakes not working after being involved in an accident

The first problem, I hope, is the terminology. There is only one power brake booster. That sits under the hood, attached to the firewall. Its only job is to make the brake pedal easier to push. It does not affect how far the pedal goes.

If the wheel broke off, I suspect the spindle or wheel bearing assembly broke. Wheels usually bend. Regardless, if it got hit that hard, my suspicion is the rubber flexible brake hose got torn off. It's odd your mechanic would let that go unrepaired and expect you to drive away.

That hose is not real difficult to repair, especially on a car as new as yours that will not have much rust. What you should be aware of, and for future reference, is crud and corrosion build up in the lower halves of the two bores in the brake master cylinder where the pistons do not normally travel. When you pushed the brake pedal all the way to the floor, you ran those pistons, and their rubber lip seals, over that crud, and that may have ripped them. This is rarely a problem when the car or the replacement master cylinder is less than about a year old. It does become a problem when do-it-yourselfers or inexperienced mechanics use a helper to pedal-bleed the brake system and they push the pedal all the way to the floor. The damage can also occur when a driver is surprised by a sudden, unexpected leak.

The symptom of a failed seal in the master cylinder is the brake pedal sinks slowly to the floor, and that often does not show up until two or three days after the leak was repaired. Many conscientious mechanics who have your best interest at heart will usually include a new, (rebuilt), master cylinder in a repair estimate when there is a chance it was damaged. They are not very expensive, and do not take real long to replace. It is hard to say if your car will need a replacement, but it is best to simply be aware of the possibility. Too often a mechanic will find a replacement is necessary after the other repairs are completed. Naturally the customer assumes he did not diagnose or repair the problem correctly, or he is trying to sell unneeded parts, but that is not the case.