The other options don't make sense
Even Ebola, polio, bird flu, and small pox leave survivors. AIDS would have probably burned out without modern medicine delaying deaths or the needles that helped spread it. Diseases tend to evolve into less deadly forms as it increases the odds of spreading.
Previous climate changes did not wipe out mammoths.
Humans coexisted with large game animals elsewhere.
If mini-elephants can evolve on a small island I doubt habitat reduction would cause extinction unless it was radically fast such as after an impact.
Combination? Didn't those same factors exist elsewhere?
I think the impact theory is the most plausible, but absence of evidence must be addressed by finding supportive evidence.
Regards,
Mark