If the Yautja mount a full scale attack on Xenomorph Prime what would happen?

Obviously if the Yautja bombarded from the motherships, the Xenomorphs would have no way to reach the motherships and would likely retreat underground. If the Yautja lacked weaponry capable of simply destroying the planet (Which is unlikely, chances are they have some sort of weapon capable of world-destruction) they'd have to go down into the tunnels to clear out the Xenomorphs themselves, which would be where it would become open warfare and the Xenomorphs would likely use their environment to their advantage.
There the battlefield would be even, although enough Yautja probably could still win, with their long range weapons and personal nuclear devices and whatnot. Although judging from the Yautja's way of life, they're much more likely to just go down on the planet and fight honourably instead of bombarding it from orbit.

In AVP WAR the predators abandon honourable combat when the goal is not sport but total dominance. Therefore in a full scale assault the Predators would easily kick the Xeno's tails.