So the Numbers coils can create copies of reality that enact different scenarios, and exists as long as the coil is working. The entire Grendel Unit, except for Kyouma, was (presumably) wiped out by the destabilization of a Number. What if the effect of the Number created a reality overlap, making it so that the Kyouma we see and follow throughout the story is not the actual Kyouma? Maybe Our!Kyouma is a copy, similar to what happened with Shiro Kamiki/Shijuro Sakaki. Or Our!Kyouma could be a survivor of the Grendel Unit who was rewritten into reality to be Kyouma. Whatever the case, Real!Kyouma is probably dead. And if that Number coil is still working, then it's all the more reason for Kyouma to find the coils, so he can end the illusion.
- Jossed. It really IS Kyouma, as shown when he defeat Haruka's threat, and ends the Easter Island anomaly for good in Chapter 74. He's still with the rest of the surviving Collectors, and is shown to have come home with Mira in Chapter 75.
We still don't know what really happened during the operation. And creating Mira may be the attempt of Dr. Yurizaki to keep her promise with Kyoma.
Considering all the eldritch abominations that appear when a coil malfunctions or is destroyed, Dimension W seems like an awful place to come into contact with. Not to forget the alternate reality ghosts who have gone insane and developed a taste for torture and human flesh.
The dimension "W" has a corrupting influence on humans when accessed with modified or third-party Coils. The Coils were based on Lemarchand's boxes with the gateway into that hellish dimension "W" replicated by technology instead of magic, but when the safeguards and limiters of official Coils are bypassed, the "demons" manage to get through and wreak havoc on the human world. Later, someone had the extremely smart idea to use that "hell" dimension as hyperspace, but of course the energy shields weren't enough to repel these weird entities and first the ship and then Dr. Weir got possessed by them.