It's likely this has been asked before, but I can't find it:
Does the Sorcerer's (Philosopher's) Stone protect against non-natural death? I.e., getting hit by a bus, Avada Kedavra, falling off a building?
The books are frustratingly vague on this point, saying only that the elixir only gives "immortality" or "stops you from dying" without spelling out exactly what that means.
“A stone that makes gold and stops you from ever dying!” said Harry. “No wonder Snape’s after it! Anyone would want it.”
To me that reads as though it's impossible for the drinker to die, a la Tuck Everlasting (albeit with the need to constantly drink it), rather than just preventing death from old age. But it can be read both ways.
On the other hand, Dumbledore's language in The Half Blood Prince suggests the Stone only prevents death from old age. But again it's a matter of interpretation:
"While the Elixir of Life does indeed extend life, it must be drunk regularly, for all eternity, if the drinker is to maintain the immortality. Therefore, Voldemort would be entirely dependant on the Elixir, and if it ran out, or was contaminated, or if the Stone was stolen, he would die just like any other man.
Making things more confusing is that we see Nicolas Flamel in The Crimes of Grindelwald and he is very old in appearance and visibly grimaces whenever someone goes to shake his hand, with a comical crunching noise. That could mean that Flamel just happened to drink the Elixir when he was old, and the crunching means he could be damaged by external means. But I interpret it as meaning that he aged "normally" and physically has the body of man who is hundreds of years old but is completely impervious to death.
He also has this line:
I’m afraid we keep no food in the house.
While not stated outright, the most obvious explanation is he keeps no food because he cannot starve to death. So it's not just old age that the Elixir prevents death from.
The honest answer is we don't know. But I'm leaning towards the notion that continually drinking the Elixir of Life makes it absolutely impossible for you to die through any means.
No. All the evidence points to it only protecting one from dying of old age, or strengthens one who is not going to die anyways.
The main evidence to this is that it is often stated by Dumbledore that there is no known way to survive Avada Kedavra. Yet there should be a way - the Sorcerer's Stone! This implies that it doesn't work to stop all ways of dying.
A possible additional piece of evidence is HPMOR's question on Nicholas Flamel: Why isn't Flamel considered a murderer for not giving his stone to St. Mungos? If it doesn't prevent non-natural death it may explain his actions.