That's a bit pessimistic. If you can do 10^10 years, you can go out to a red dwarf and stick around 10^13-10^14 more. And with a few small mods you can go further. For example, should you want a "small, slow" world, consider what what would if you "turned off" a star (e.g. tore it apart until it could no longer sustain fusion) and burned its fuel more slowly, in engineered fusion reactors. The sun has a natural lifespan of a few billion years; but consumed at a relative trickle of 10^17 W (the part that strikes the earth), there's enough fuel for about 10^21 years. (Conversely, you could grow your world until it matches the power output of a star, like a Dyson sphere. Urban planning decision.) The part that humans actually metabolize is barely 10^12 W (10^26 years in bubble chambers), and non-organic human simulations could do better. And there's a lot more hydrogen where that came from... and human knowledge of this universe's physics is clearly incomplete (what the hell is dark energy?)