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U235: Yeah, that's true.
Even if his body had survived and didn't get affected, its really odd how MC's mind is still stable after 100 Million years of isolation (unless some special magic is in place which allowed MC to stay sane and unchanged).
There is already another series were a Ordinary Mage accidentally created a medicine which granted him immortality (with an unchanging appearance) and is nearly 4000 years old by the main story point. And there is some characterization of the MC in that series which denotes the change in mind after living for so long.
The concept of that series (from what i understand) is that any type of person can achieve anything they wish, but a Genius is able to achieve things much faster than normal people (example, MC being a normal Mage, it took him 200+ years to research Teleportation Magic on the same level as a group of Genius who took around 7 years to reach the same point).