Plenty of people (not tons, but many) experience loss of neurons through injury, disease, or aging. We generally consider the person to be the same person, even if their personality changes.

Likewise, as you grow in childhood, you create many many neurons. Again, you are still you throughout the experience of growing up.

I suspect in your thought experiment you'd remain you throughout. Honestly, a community I bet does a lot of thinking about the self and what makes you "you" is the trans community, given their experience grappling with bodies and identity already.

My grandma got dementia, and she has been deteriorating quite a lot just now at the hospital to the point where she is unrecognizable. Yes, technically she is still my grandma, but at the same time she is not. I hope you understand what I am trying to get at.

(Of course I still consider her my grandma and she is being cared for just as much as she would have been years ago. It just saddens me that I cannot have the same or similar interactions as I could have some time back.)