Well Xizer, mate, you asked for some of my insight on the matter, and well, here goes
I believe the Empire would have achieved a Pyrrhic, yet decisive victory.
I believe the war would have been predominantly fought in the northern outer-rim regions (Yaga Minor etc) and the Vong's advance would have penetrated no deeper than Anx minor or so.... (the mid-rim).
I believe, that although there would have been resistance, the Mon calamari would have been kept at bay, and their ships would have also been used in the imperial star-fleet, or their technology would have helped the Empire improve their ships' shielding. The Corellians would have remained very loyal, providing many more corvettes and further technology. The bothan spy net would have been used to the empire's advantage also.
However... the major thorn in the Empire's side, may have been the dislike of alien species... something which the Vong may have played upon... and used as propaganda, to promote insurrections and widespread rebellion of alien species, especially once the Vong realised, that head-to-head battles with the massive Imperial star-fleet was not the best tactic.
Had the Emperor been more lenient towards more non-humans, his army and control would have been far greater.
Vader may have even found Luke, and trained him in the Sith ways.
Viruses may have been invented, to deal with some of the Vong, but they may have caused more harm than good. I therefore think there would have been a series of 10-15 major battles, on land, and in space, as well as sea. During which, casualties would have been enormous, however the Empire would have also had many other vehicles, and older support, such as battle droid armies and hailfires etc, which could have been put to use as a first line of defence, in the outer rim (from the region under the PA). I also believe, fighter technology would have improved, and fighters such as the X-wing, would have proved pivotal, but for the Empire.
Many worlds, however, would have still been ravaged, by both sides.