Eh, not 100 percent. I don't know how you're taking all geologic hypotheses as gospel...probably because you're not a geologist. It's called multiple working hypotheses for a reason.
On the plus side, your paper does note that a methane doomsday scenario is highly unlikely, which is a good thing.
I got that doomsday scenario from Hansen's "Storms of My Grandchildren." It was written about 2007 or 2008, so he may not have been aware of this when he wrote it. At the moment, even if the gun fires, life will survive it whether we do or not - there isn't enough CO2 in the air to set off an irreversible greenhouse effect. But that's at the moment; we are adding to what's there all the time and we will reach the point where such a disaster becomes possible in a few more decades. I, for one, would prefer to run no risk at all. Any chance of destroying all life, no matter how small, is unacceptable.