I would never contemplate re-starting an engine after a fire warning in except the most dire of emergencys. I would consider failure of the remaining engine/s a dire emergency, but even then, hoping against hope that the original fire warning was a false alarm. And if the original fire warning was genuine, it WILL inevitabely catch fire again, and you're now in a much bigger pool of excreta, because you've already blown your extinguishers.
What Trash Hauler said about oil supply is true, but frankly, from the performance aspect, you'd be better off if the failed engine quietly siezed, because a siezed engine has less drag than a windmilling one.
Regards,
Old Smokey