[@Aristocles]Not quite. That was stated at one point in the lore, but they did retcon it. The majority of the Skirmisher units in the Covenant military at the time were wiped out on Reach, but the subspecies is still around, in lesser numbers. A unit of Skirmishers would not be likely to be seen, but individuals may still ally themselves with various factions, or take up mercenary work. 

I am also working on a response, but I keep having to step away and do things.