i dont understand the question.
how do you want them to be revived?
after how long? depending on what?
here's a hero revival system:
http://world-editor-tutorials.thehelper.net/revive.php
if you want it for just an individual unit, do something like this:
unit dies
dying unit equal to ***
wait ## seconds
create 1 *** at **point
or something like that. be more specific if you want something different.