It is to souls though, Mimara second baby was still born, the soul that encounters him goes no further.
It's a strange thing. Yes, the No-God does something with birth, though we don't know what. But just by being there it doesn't close the world. Sorcery is contingent on the Outside and still works, the Gods are able to act and were able in the First Apocalypse, I'm pretty sure Ciphrang can still be summoned, and also, as dragharrow succinctly put it above, if it was enough for the No-God to just exist to prevent souls from going to Hell (or, much less likely, Heaven), the whole Apocalypse and 144k thing would've been totally unnecessary.
Considering all of this, I don't think it is correct to say that the world is closed in any way.
It stops all souls from going to the outside though.
The No-god has a shelf-life, exposing the code allows the no-god to make permanent the effect.
What do you think "the soul that encounters him goes no further" means in your context?
Obviously this is all speculation as no one really knows. For the purpose of debate i'll assume my weighting is correct (probably isn;t)