there is nothing called officially in my opinion.
you can call a coin dead for many reasons for example:
- when the developer gives up on his own project and nobody else is interested in picking up where he left off.
- when the price goes to 1 satoshi and there is no buy orders and nobody is buying from the asks either.
- you can even go as far as calling a coin dead when it is getting dumped real hard down to 1 satoshi
- technically a coin is dead if there is no one mining it and there is no full node of it available any more.
You missed the one that really kill the coin , for me is when all the exchange delist it, that is when the coin die, without an exchange yu have nothing no trading, and trading here simply does not work well, another one is when the blockchain isn't working and it is not fixed, because of a bug or other things