If Biden wins presidency & at some point alleged dementia gets too bad, would VP automatically take his place?

There is a process in place to deal with the situation where the president becomes incapacitated. So the Vp would not move up automatically but would when the requirements of the law are met. 

Of course.. didn't you know that is the commie dems plan.. they do not Biden to be resident.

HE WON'T WIN SO STOP WORRYING"

I saw Biden on the news a few days ago, riding his bicycle, and I watched Trump two months ago have trouble walking down a handicap ramp at West Point. 

If anyone is suffering from any type of age related medical conditions, it's Trump. 

But to answer your question, the VP always takes over when the president can't do his job. So even if Biden was hospitalized for COVID-19, but not dead, the VP might be sworn in, temporarily, as acting president.

Are you kidding?  Are you really too young to remember presidents like Clinton, Dubya and Reagan?  Those guys were basically vegetables before they were even sworn in, then things got really interesting, and they still finished their terms.

Old Joe would have to exhibit less brain activity than a houseplant before they'd hand the job over to Kamala.

It was rumored Ronald Reagan developed some dementia while in office.  History says his wife took over many decisions and is perhaps why he is remembered as such a great president. If Biden is already exhibiting signs of dementia perhaps he is not such a good candidate. 

Not 'If' but 'when' Biden zonks out and can't get out of bed any more.. Yes that is what the VP is for.. Automatically..

The VP is the next line; but while the procedure to remove a President who is 'incapacitated' is spelled out in the 25th Amendment, it's never actually been done.

If a president can’t serve his duties until the end of his term, the VP will take over. That’s why Biden wanted a VP who’s ready to take over if he can’t complete his term. 

Congress can also have him removed if they think he’s incapable. 

of course and thats almost a certainty imo ... biden can barely complete an intelligible sentence ..