And since when did learning a place mean learning a place couple of hundred feet below you?
And don't tell me he can open gateway from ship to sea bed, then another into space! His ship will be flooded instantly if he does that.

The same problems are going to face him even then!


Uh... what? Where is this? He can't even see five miles away to weave something there, let alone know a place five miles away by standing on one place!
Never knew you were in the business of manufacturing hyperbolic nonsense to cover your point.

I think you're unaware of the kind of forces we're talking about here. This is water going from high pressure to an infinite vacuum. Its simply going to explode out of the gateway, promptly becoming gaseous. And the shock waves of the explosion will definitely carry more than a mile. And who knows if even Ishamael can ward against such forces?

Assuming these Deathgates can be made non-random, they will eventually reach the sea bed an cut through it, now poring out magma into space, but also opening up holes in the earths crust to allow the water to go there, flash into vapour, and move up into the atmosphere.
I'm not even going to try to predict what exactly will happen at such a point. With the earth losing so much mass so quickly, who knows how its orbit with the sun, and the moon's orbit, will be affected?
Civilization will probably end up getting destroyed, but will that mean it is the end of time? Even if humankind is extinct, the DO may not get free. After all, we saw mirror worlds with no humanity, and total destruction, yet the DO wasn't free in those.

And if you'd thought a little beyond "I want cool villains", you'd have seen the ludicrous nature of your "ideas".