This is another one of those things that can go wrong with using valet parking services.
Imagine if you have to catch a plane and this happens to you. It's a good idea to bring a spare key with you! If you don't have a spare, here are your options:
Call somebody at home to bring over a spare key, or have somebody drive you home to get the spare. (Your house key is not locked in the car too, right?)
You take charge and tell the valet service to bring in a locksmith immediately, at their expense. And you demand a refund of all parking fees paid due to the inconvenience and aggravation caused.
You allow the valets time to attempt to open the door.
You have it towed to the dealer.
You stand around doing nothing.
Any high volume valet operation will probably have a thick, sturdy wire on-hand that was purposefully made for unlocking car doors. It's easiest to use if the window is cracked open a little. If not, they are going to use brute force to squeeze that thing inside the car. If this is what's happening, it might be best to insist they stop the work and call a locksmith. They probably have a locksmith number written down somewhere.
If the valets are standing around bewildered about what to do, then it is up to you to make decisions.
Can you get your hands on another key? This is probably the best resolution. If not, demand that they immediately get a locksmith there and demand that they will pay for it.
After you are back in your car, demand that your parking is free today — because you hired them to competently and safely park your car, not burn up your time and annoy you.
You also insist that you want X number of free parking transactions over the next month. This gives them the opportunity to win back your loyalty. (Otherwise, you will be inclined to park elsewhere when returning to this area.)
If the locksmith can't get it open, then the last resort is to have the car towed back to the dealer for them to figure it out. This will be the most expensive way to fix the problem. Deal with the valet manager. Get promises in writing that they will pay.
From my experience...
There are actually cars that will lock automatically 60 seconds or so after you exit the car. That's not a good thing if the key is still inside.
On a busy Saturday one of my young co-workers was dealing with the emotional turmoil of having girlfriend problems. He should have stayed home, because he locked somebody's keys in their car. We had to get a locksmith. An hour or so later... he did it again!
He locked keys inside cars TWICE in one day.
We had to get the locksmith again.
(The boss was angry.)
I never locked keys inside a valet car, but I did break a key off in the ignition of a car... while it was in the on position (draining the battery)... while the car was in rising flood water from Hurricane Sandy. It was an old, yet pristine Rolls Royce. (Everything worked out okay.)