Hello Jenny
I don't have any specific information, off the top of my head, regarding F Troop in particular, I'm afraid. I can tell you about the 15th Hussars in general, which may or may not be known to you (copied from one of my earlier posts) ...
They marched on Kandahar in December 1878/January 1879, with two squadrons of the 15th seeing action en route at Takht-i-Pul and in the Ghlo Pass (not sure if one of those was F Troop or not); they were at Kandahar for just a few days before they accompanied General Biddulph up to Khelat-i-Ghilzai, stayed there a fortnight, and then returned to Kandahar. Soon after they were sent back into the Pishin Valley, opening up a route through Yargistan and then returning to India (Mirat). They started for the Afghan border again in August 1880, pausing at Quetta and eventually reaching Kandahar after the campaign had been effectively ended by Roberts' victory at the city earlier on Sept 1st. They were back in India in October. They went on to see service in South Africa in 1881 before returning to England.
Out of interest, the 15th Hussars suffered greatly from the cold at the Bolan Pass on their first advance to Kandahar, and greatly from the heat at the same location on their second advance in August 1880.
Having 'Nil' under Gallant Conduct is not at all unusual, so it's certainly not a sign of anything. I'd also have to say that drink and disease was very much a part of army life in India - so, as you suggest, don't be too harsh. (Demotions, prison and court martials would set him apart, though with enough company, for sure).
Best wishes - Garen.