While Battle of Hoth was considered a major victory for Galactic Empire, Empire did fail to fully crush Rebel Alliance because rebels (mainly, leaders) successfully escaped (probably, this is the reason Darth Vader executed Admiral Kendar Ozzel).
Rebel escape was always a possibility. Why weren't there Interdictor-class Star Destroyers (AKA, Hyperspace Interdiction Cruisers) in Battle of Hoth?
I have almost forgotten, but rebel fighters did provide some cover against Empire fire. But, I don't think it'd work on Hyperspace Interdiction Cruisers as they could pull a ship from hyperspace.