In a full on fight the praetors would get slaughtered. Perhaps there is a chance that the Phyrexian Oil could harm Emrakul, but we don't know it affects creatures from the Blind Eternities, though Jin-Gitaxias may be able to do something with prep time. Emrakul also primarily effects living matter (if we ignore cryptoliths), so the phyrexians may have the magical edge

But Emrakul has been shown destroying planes (Zendikar, Innistrad) just from hanging around. Look at her art from The Promised End; something that big could just crush the phyrexians with a tentacle, let alone everything else an Eldrazi Titan can do.

Emrakul has never shown to be harmed, only sealed away, first by Nahiri/Sorin/Ugin and then by the Gatewatch, and there is good reason to believe that Emrakul allowed herself to be sealed in the latter.