Originally, if this wasn’t a special mini comic, I would have had the Doctor fail at bringing Dinky back and have the crack close.  
The Doctor would have been forced to use his Tardis to travel 10,000 years to the future when the crack opens again in order to find Dinky. However in his search for her he had to go in even deeper and colder places of the ice city in order to face Dinky as a full grown queen of the ice ponies. Which would be much more difficult for him to break the spell and return her to her normal state, and also having less than 24 hours to do so before the crack closes for another 10000 years. If the Doctor wouldn’t be able to bring her back now, he never would.
 
By his first meeting with her the first two words to leave the Ice Queen were
 
‘‘Doctor Who?’’