Think, people, we're going up against 3cm tall plastic and metal figures! The worst they could drop on us would be a Pulsa Rokkit, probably. Hell, they don't even have a Gargant. Just get an army to march into the greened area and blow them to pieces. Maybe even just give them a big area so we can all have a good time watching docos about them on TV and let people come in every "Greenskin season" and shoot a bunch. Doesn't matter if we almost wipe them out, they'll grow back. Of course, you'd have to bring in military stuff like bombs to drop on the really nasty stuff like Stompaz, Pulsa Rokkitz and Ghazghkul. In this event, I want a pet Squiggoth.
If it's at full scale, then depends how big the Waaagh! is. If it's big enough to beat with nukes and most of the armies of the world or smaller, then we're fine. And I'll want a pet Squig, if that's the case.
If it's bigger, then we're royally stuffed. Pack as many people as you can in spaceships, and then get them offworld. Maybe subs if they have boats but only one or no submarine(s), but also large ships with a bunch of weapons if they have no water vehicles.
That third paragraph is being very optimistic, BTW.
This is a warhammer forum. Everything is a military operation.
I have spent the last 25 minutes doing reconnaissance on my kitchen for operation: Cup of tea.