Dead coins don’t just come back to life. If developers are nowhere to be found and it has been delisted from every exchange, it is time to give up hope. Depending on whether it is the native blockchain itself that is dead or just a token built on a chain, there could be major security issues. It would not be very expensive to do a 51% attack on a dead blockchain.

Usually, before a coin dies, there are warning signs and this is when you should have cut your losses and dumped it. I have not seen a successful revival of a dead coin, but there are some coins that are running on life support that keep going for many years. I wouldn’t count on them making a comeback and would just look for a way to cash out if they still have any value.