Is there a way to find a dead or offline iPhone?
Unfortunately no, all of the methods for locating lost/stolen iOS devices depend on the device being on and connected to the Internet in some way. If it is not on and/or not connected to the Internet in some way then you are just as likely to find the Boy Scout knife you lost when you were 8 the same way.

Note I am not being facetious here, just trying to be clear.

If someone finds the phone and decides to charge it up, it may reconnect to a network somewhere and become findable again. I would log on once a day and see if that has happened. That chance of that happening? Well your guess is as good as mine.