There isn’t a single mention of dementia in that paper. The only mention of stroke is associated with
cigarette smoking. It talks primarily about nicotine’s effect on the vascular system and the effects seem minimal, even in mice.
Here’s a pretty comprehensive list of the benefits of nicotine and the lack of significant side effects.
https://gwern.net/nicotine#benefits
Here’s the conclusion he came up with after significant perusal of the research
“Nicotine is pretty much harmless, the studies are clear, the relevant areas & studies comprehensible with not too much work, and I feel I can discuss it with a clean conscience. Really, about the worst you can say about pure nicotine use is that it might be a gateway to tobacco or that one’s blood pressure might increase, which are issues that can be easily addressed empirically via additional studies/surveys or by eg. measuring one’s own blood pressure after taking nicotine, respectively.”