It's not entirely unreasonable to think there will be life here until the sun swallows the earth up entirely
Actually, it is entirely unreasonable to assume that. For hundreds of millions of years before the Sun "swallows the Earth" (itself still only about a 50% probability ; predicting the exact degree of stellar swelling in the red giant phase is beyond current astrophysics), the Earth will be baked to the degree of Mercury, then Venus, then maybe to the point of a magma ocean then erosion by the plasma of the Solar atmosphere.
But hundreds of millions or billions of years before then, the slow increase in Solar output will increase terrestrial temperatures (research the "faint young sun paradox" for more info). Note - we're talking about changing Solar luminance, not changing the Sun's size. The size may change a little, but only a few %. The big growth of the red giant phase is still far in the future.
You may have noticed that to maintain our current approximately 15 K of global warming (from atmosphere-free equilibrium to our current temperatures, globally averaged), over the last couple of billion years the carbon dioxide content of the atmosphere has gone down from multiple percent to multiple parts per million. Eventually the reduction in global warming achieved by that reduction in CO2 will stop - because there won't be any more CO2 to remove from the atmosphere. At that point, the increasing Solar flux will start to increase surface temperatures (regardless of what humans do about it, except geoengineering) and the next greenhouse gas will start to take over. That is water vapour. And as temperatures rise, the oceans will get hotter, leading to more atmospheric water, leading to increased greenhouse effect, leading to increased temperatures. The observant may spot the presence of a positive feedback loop there.
That is when it gets very hard to predict exactly what will happen. But an increasing trend (driven by the laws of nuclear fusion in the core of the Sun) driving a positive feedback loop is a recipe for runaway. Best current estimate is that it'll happen around a billion years from now (+/- 20% ?)
When that feedback takes over, the Solar system will have two baked-atmosphere planets in the inner system - Venus and the Earth.
Are you aware of life forms that can live in an atmosphere of super-critical steam and nitrogen?
Actually, I'll revise slightly. I can conceive of genetically engineering organisms that could survive in the atmosphere by using gas bladders to balloon to a pressure level where the temperatures and pressures are manageable. Te bladde would probably make sex difficult. But if cephalopods can invent "copulation by guided missile", I don't see that as an insurmountable problem.
Can I conceive of such evolving naturally ? Hmmm, much harder. Portuguese Man o'War might be a workable model. Vertebrates that can give birth and nurture on the wing ... that's a big ask. I'd hesitate to say it's completely impossible, but it's a big ask. I note that we don't see seasonal (in the sense of perihelion/ aphelion) colour changes in the clouds of Venus, suggesting that Venusians of 3 billion years ago failed to make the transition when the time came for them.
The billion years in the future date relies on the details of atmospheric modelling (much more complex than nuclear reactions) ; but that the seas will boil long before the Sun starts to grow appreciably is a robust result.