18 I taught I read somewhere that even when they would be sealed they slowly destory Zendikar, at a speed of a few million years or so(thus it is not that big of a deal)18 (you increased it by 2)
At least, that's what happened the first time they set up the hedrons. After drawing the Eldrazi to Zendikar, the hedron network then sealed them beneath the world's surface, where they couldn't do much. Bug the heck out of Zendikar itself, sure; but not actually consume its energy.