Let’s say we left one single very smart guy (not necessarily with the knowledge: they may be able to understand hard stuff when taught it, but not know it already) alone on a copy of the earth. That person is also immortal. Could that person, by themselves, gain back all knowledge, maybe also experimental, or even surpass that is already available to us right now, before the planet gets inevitably engulfed by a sun turning red giant?
I’m going to say no. A body immune to life threatening illnesses means they cant properly test medicines and get them right. And if they’re not immune, exposing themselves to life threatening illnesses will put a stopper on that when they fail to get their medicines right on tbe first go.
they could be tested on animals though. granted, they may work differently on animals, but they might be smart enough to work something out