assuming some survive to the point humans can tame or domesticate them would they be useful to an Ancient military power?
at that size they can be used to plow and pull carts etcon average, 1.72 m (5.6 ft) tall at the shoulders and 760 kg (1,680 lb) in weight
I think this should be in ASB.
Human actions likely caused the ultimate extinction of mammoths, so no, I don't think it should be ASB.
I'd argue that's debateable. Humans and Mammoths lived alongside one another for thousands of years then at the beginning of the Holocene they went into a rapid decline.
I'm sure Human's had an impact on them, but we have to remember that the last Mammoths to die out did so on Wrangel Island without the input of man. I'd argue that primarily they were unable to cope with rapid climate change, although I don't admit to being an expert on this period.