2.8 billion years[0] is the high estimate before _all_ remaining life on earth goes extinct. Likely including these little buggers.

[0] https://en.wikipedia.org/wiki/Timeline_of_the_far_future

based on our current knowledge, not only of the science that we can extrapolate to the future, but of our technology and how we will apply it

note that that list is all negative things we suspect will happen and include no accounting for our own intervention in matters

I'm not sure how anyone's intervention could ever withstand some of these effects.

I could foresee maybe a sun shade of some sort to help mitigate the increase in temperature, but at some point the sun is going to envelope the earth.

Also, this several billion years into the future. Anyone left wouldn't be anything you could remotely call human. Evolution hasn't stopped in humans.

iirc we could plausibly move to Titan and live off nuclear energy

Why not just move the Earth? You could do that over a few million years using a gravity tractor.

https://en.wikipedia.org/wiki/Gravity_tractor

Honestly I don’t think anything could extinguish all life on earth short of maybe 20 comets hitting earth at the same time or something.

I wonder how long it'd take for life to leave after Earth leaves the goldilocks zone. How much life would there be after the oceans have evaporated and stripped into space? If life could evolve to not require water at all, maybe it could survive until the sun physically envelops the planet.

20 comets (or asteroids) wouldn’t even come close to doing it. Events like that can cause extinctions of many ecosystems, by many others will be essentially unaffected. Microbes in the sediment below the seafloor are a good example. They wouldn’t even notice the comets.

The slow and inexorable brightening of the Sun (it's already 30% brighter than when it settled onto the Main Sequence) will eventually cause a runaway greenhouse effect. The oceans will all be converted to steam and the surface temperature will be far beyond what life could survive. After that things only get hotter until the Sun enters its end stages and leaves the Main Sequence.

A hot surface does very little to life several miles below it.

Since heat is flowing out of the Earth, the temperature below will eventually become hotter than the temperature at the surface.

I remember reading somewhere that that may have saved life on Earth at least once.

Think bigger with your mass extinction events! Maybe a rogue blackhole zipping through the inner solar system and ripping the crust off the planet like a ripe tangerine.