About the Gurkha beheading: this is one of the big reasons why so many prominent targets were beheaded in the good old days. In a world without photographs, taking the head to someone who knew him was the surest way of confirming that the deed had indeed been done. When Yazid's Ummayad forces killed Hussain at Karbala (now remembered as the central event in Shia historical memory), they beheaded a person who was, after all, the beloved grandson of the holy prophet of Islam. This was not just (or even mainly) an expression of their barbaric nature. It was the norm to cut off the head of the rebel and take it to the emperor for inspection, confirmation and reward.
When Aurangzeb overthrew his dad and killed his brothers to become the Mughal emperor of India, one brother (Shuja) escaped to Myanmar. He was apparently killed in a skirmish there, but no one brought back a head (to the Raja of Arakan, whose people killed him; or to Aurangzeb, who was not directly involved in that skirmish). As a result, rumors of his return unsettled Aurangzeb's officials for years. ..Much better for the imperial government if that head had been cut off and brought for display.