What would be the extent of the feedback on climate of unattended deaths event?

Question

Being given that decaying corpses will stop emitting digestive metane, but would release huge amount of methane during their decaying process, I was wondering if this could be considered among the Climate change feedback loops?

To illustrate this, let's just say that scenarii for year 2050 include possibility that population (and livestock) would collapse in a decade. We may have something like 200'000'000 tons mammals decaying in a 5-10 years span... This is not even a quarter on below image, but already so many methane released at once!

Edit: I am not looking for existing signs, I am thinking of the effect of billions of mammals death on the greenhouse effect caused by the consequent huge methane release.

(copied from https://media.treehugger.com, credits XKCD)

Answer 1

Mass of Earth's atmosphere: $5 \times 10^{18} kg$

Concentration of methane in Earth's atmosphere: $1866 ppb$

Mass of methane in Earth's atmosphere, present day: $9.3 \times 10^{12} kg$ = 9,300,000,000 tons

If all those dead mammals were composed entirely of methane, they would increase the atmospheric concentration of methane by about 2%. They aren't, and (as @trond hansen commented) most of their carbon would be converted to $\ce{CO_2}$ with a 30-fold smaller global warming footprint.

So, I think it's safe to say the impact of decomposing mammals would be relatively small.

Worry more about effects on plants, which constitute 80% of the Earth's biomass; bacteria, which constitute 15%; and fungi, which constitute about 2%. The entire animal kingdom amounts to much less than half a percent of global biomass, and half of that is arthropods (which have their own concerns for the future).

(Source: figures from The biomass distribution on Earth, Yinon M. Bar-On, Rob Phillips, and Ron Milo, PNAS June 19, 2018 115 (25) 6506-6511; first published May 21, 2018 https://doi.org/10.1073/pnas.1711842115)