I think only the Sikh Empire had any chance to survive as a princely state. The Mughal Empire was an empire that covered most of the subcontinent and the British could never allow it to return to their former glory. They wanted to maintain a nominal emperor as long as he served their interests. When they realized that he could become a weapon in the hands of their enemies, they got rid off him with no hesitation. Then the case of the Maratha Empire. When the British started their struggle for the domination of the subcontinent the Marathas were their close contestants. They were the strongest Hindu Power who could challenge them in future. The British could never allow a unified Maratha Empire who may grow into an all subcontinent power. They tolerated Maratha generals like Scindia, Gaikwad etc. as kings because that served their aim of destroying Maratha unity. On the otherhand the Sikh Empire would be confined to Punjab and nearby areas. There was no chance that they may spread to the South or Bengal.