Even if the normal rate increased immediately when a new channel gets added (it doesn't increase immediately, though) the price lock would protect you from the price increase. That is the point of the price lock. However, in this particular case with channels being removed, the RSN's are not just any ordinary channel, but rather among the most expensive channels in the package. So, hypothetically, lets say that the normal package price decreases by $5 per month due to the lack of RSN's. The price lock seems to be a $20 discount off the price of the package at the time you signed up for it. If the regular package price had decreased immediately at the time of the RSN's removal, that may be okay. However, that decision to decrease the price seems to have been delayed. In the meantime, you have people signing up for a price lock expecting a $20 discount, when the regular price is about to automatically include a $5 discount. So, people who sign up for the price lock before the regular price changes are, in effect, only getting an additional $15 discount, while people who wait for the new lower regular rate to go into effect before signing up for the price lock get the full $20 discount for the exact same programming package.
I would be surprised if Dish drops the price. They are already less that A&T and many cable companies. Plus Dish as well as others have lost some subscribers to streaming.