Where in his Bani or his writings does Guru Gobind Singh give any indication of having that motive for helping Bahadur shah? You should not impose your own motives/agenda on Guru Sahib and assume that you speak for him, particularly when there is zero scriptural evidence for your position. Neither is there any historical evidence that I'm aware of - the histories say that Guru Sahib's motivation for allying with him was the condition that non-Muslims would be treated fairly under his regime. So, I ask you, how do you know that was Guru Sahib's motive for helping Bahadur Shah?
The Dogras were the most immediate cause of the empire's downfall, but the fundamental cause for the collapse of the Sikh Kingdom was Ranjit Singh's fatal decision to make himself king of the Sikhs and replace the Khalsa's republicanism (Sarbat Khalsa, Gurmatta, Jathedari) with a system of absolutist monarchy which centralized all power in his hands - this had no place in a 'Sikh' nation. His miscalculation ensured that the kingdom would all but fall apart his death and be vulnerable to vultures, particularly in light of the uselessness of his heirs.
I disagree veerji. This Sikh kingdom would never have become as powerful as it did if not for non-Sikhs. The Sikh Empire was so successful while Ranjit Singh was alive precisely because he managed to integrate and secure the loyalty of the Punjabi musalman who constituted most of his subjects - and thereby ensured economic productivity and public order. The Khalsa army of the Lahore durbar was also not just made up of Sikhs - all cavalry were Sikh, but virtually the whole of the artillery was Muslim, as was a significant portion of the infantry of the regular army (included Pathans, Punjabi Muslims and Gurkhas). Secondly if not for the induction of non-Sikh European officers into the Sikh army, it would never have relinquished its fixation with irregular cavalry or its revulsion at the idea of infantry. Without the innovations of these non-Sikhs, therefore, the Fauj would never have advanced to first rank among the armies of Asia. An army composed entirely of cavalry is fine when you're fighting a guerilla war, not so much when you're building and defending an empire against men with guns and artillery.
Furthermore not all non-Sikhs in the kingdom were disloyal to the durbar, and not all Sikhs were loyal. The Muslims of Punjab routinely resisted the calls of the Afghans (and later, the mutineers of 1857) to join them in jihad against the infidel Sikhs. The Fakir brothers (Muslims) were loyal to Ranjit Singh's memory to the last, as were several of the other Hindu Dogra generals of the Khalsa army (Dogras are a race, not a family. It was one family of Dogras in particular which caused most of the trouble). And while there were good, loyal Sikh nobles such as the Attariwalas and the Nakkais, there were many more who were fickle and treacherous. Rani Jindaan was notoriously corrupt , as were the Sandhawalias, who murdered Sher Singh, the only successor of Ranjit Singh with even a shred of competence, by blowing him to pieces with a shotgun. I think your stance is way too absolute bro.
An empire is by definition multicultural and cosmopolitan. The Vatican is not the most apt comparison here (It is a country in name only).