I've dealt with true villains before, Estro, you are not the first - and I don't doubt that it would provide an advantage to you that you are willing to make ridiculous sacrifices and take great damage in the achievment of your goals, but you have failed to address my primary argument. It doesn't quite matter if your Necrotroopers would keep fighting until they are reduced to their very base atoms, if the ship explodes before it can cut through the earth, then there's no way for your forces to launch their attack. I put forth the opinion that your ship would explode before they would be able to, because of just the sheer weight of fire being levelled on them.
I make exceptions and bend the odds for heroic things, or characterful things, or villanic things, if there is room for random chance - A grenade going off at the feet of the common soldier would kill him dead, sure, but what if it is a heroic character who hurled himself on the grenade to save his loved one? Maybe he is found dying, instead, and later saved by a miracle of medical science - or something otherwise
cool.
However, there is no such room for maneauvering in this post, it's just a matter of sheer time. You can't have your shields up because you deployed ground troops, meaning you lowered your shields to let them out. An unshielded warship under fire from such overwhelming fire as this would be dust before it could possibly drill through the very crust itself. That is my case, and it remains unaddressed.
*EDIT* Whoops, I see you did indeed initiate shields. No matter, though that would certainly improve your defences, a single Dreadnought would not last long enough to make this hole and deploy an army, I would say. That you could cave in the tunne entrance to a fortified metropolis in a single attack is equally improbable.
*EDIT 2* Saying "No Matter" rocks.