Release of all the stored methane would not cause the Earth to turn into Venus. We know this because the process has happened several times, and not only did the Earth not become Venus, it did not come anywhere even remotely close. There is no known process by which climate change would render the Earth uninhabitable.

This doesn't mean it's okay. Release of methane has always happened at the same time as major mass extinctions, possibly as the cause of it. It would create massive warming which would make large inhabited parts of the planet much less desirable, play havoc with the biosphere possibly making large areas of farmland unproductive, and in general being a massive economic drain and probably killing a lot of people.

If we talk about the 5 great extinctions on Earth to date, with 96% of life dying out after one of the great methane releases, i think our chances of survival in such an event is minimal. I don't think even a tiny group of humans could retain enough resources and technology to survive the millions of years that would be needed before life regenerates itself.

These are the methane clathrates trapped mostly in the siberian sea (Arctic ocean), where increasing sea temperatures are causing methane to bubble up to the surface in large patches (sometimes 1 sq km in size).

Runaway global warming by melting methane clathrates is known as the Clathrate Gun Hypothesis: https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

In previous mass extinctions, such as the End of the Permian, 251 million years ago, 96% of species were lost - due to a similar event: " A cataclysmic eruption near Siberia blasted CO2 into the atmosphere. Methanogenic bacteria responded by belching out methane, a potent greenhouse gas. Global temperatures surged while oceans acidified and stagnated, belching poisonous hydrogen sulfide. "

https://cosmosmagazine.com/palaeontology/big-five-extinction...

The other Arctic tipping point is because the ocean absorbs a lot more energy than ice... so once the Arctic loses more ice cover, it will go ice-free and remain that way.

Nobody knows when/if the methane problem will happen. The ice/ocean thing can be modeled.