The merchant CAN DO SOMETHING if it wants to.
I had Hilton Portland front desk mistakenly took authorization of full rack rate on a Priceline stay. I called the hotel and talked to the guy overseeing billings. He took care of it.
From what I understand, the merchant can send a cancellation on the authorization request. I saw that being done in front of me at a hotel in New Zealand - it was a 3-nighter stay on points, but the hotel was a rather upscale hotel with high rates. Upon check-out, our bill was 0, and I requested the hotel manager to cancel the authorization as we were on the road and had 3 weeks ahead of us before returning to US. She did that and handed me the proof - a receipt showing cancellation of authorization request.
Someone taught me to use a card that you dont normally use, for check-in if you expect a 0 or very small bill on check-out. Then you switch card upon check-out, so the authorization would not affect the credit limit of the card you actually use on the trip.