So how likely is Philodemus's particular story, for which we know of no other sources, to be true?This article has good observations, some of which overlap with the ones I made here. I agree that the account of Plato's last night is likely apocryphal.There are reasons to be suspicious. The death of ancient philosophers was meant to reflect their lives and teachings. If not, posterity was quite happy to invent an appropriate deathbed scene.
While we're on the subject of Plato, Roger Pearse has an excellent recent post on How did the works of Plato reach us? – The textual tradition of the dialogues.
Plato’s works have reached us in medieval handwritten copies, the earliest written around 900 AD. The dialogues are arranged into nine groups of four dialogues, or “tetralogies.”[1] These give us the works in complete form, from direct copying down the centuries. But there are also surviving fragments of ancient copies on papyrus, found in rubbish dumps in Egypt where the climate is dry, which sometimes give a better reading in this passage or that, where the text has become corrupt in the centuries. Plato also is quoted at great length by other ancient authors, and sometimes these also have readings to contribute. Finally there are ancient translations of Plato into other languages.[...]
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