[Xiammes]

Spoiler:

The Angel could have encountered a first response team trying to discover what happened/was happening. A lot of eyes must have been looking at that place and two aliens standing in the middle of nothing must have attracted attention.

I doubt they stood out, the black spot is huge, even if they were 10m tall you couldn't see them easily from the edge.

The rubble can be explained in several ways.Imagine the sphere of influence of the gate was literally a sphere(or semi-sphere), if so the tops of the skyscrapers could have been spared instant destruction at the edge of the sphere and fall down when the lower parts where sucked in. Or perhaps if the Angels were sucked in forcefully some other rubble could have travelled back along with them. Or perhaps the bombinghad crushed most of the buildings in small enough pieces to get sucked into the gate, leaving still standing structures where they were. Or perhaps imai Kami felt the place needed rubble for an extra desolate look of the place.

It would have to be a very small sphere because there is ruble near the center of the black spot, matter in fact it couldn't been a sphere, only the buildings at the edge of the blackspot would have had a chance to not be completely sucked up. Then we have the case of Iron mountain. This just points to the dimensional weapon have a very small AoE and the nuke did the rest of the damage.

It would look something like this.

Spoiler for sphere:

If you're limiting yourself to one core idea and it's variations, yes. But to me it's exactly because we don't have much to go on the possiblities are greater.

We aren't given very much room to think about alternatives. We know the Angels came through, they were hurt, and nukes and dimensional weapons were involved. It could be possible that humans somehow injured them when they came across but that's highly unlikely.

Gido did say it was his final hope but also that bringing back Kasumi is why he created the clones and preserved the gate while he was watching over Eve, so I'd say this isn't something he only thought of later after he had exhausted his other plans. I think it's a long term plan he had from the start in case the others didn´t work out.

I don't if he had the idea originally, but this is clearly is last resort as he could do nothing else.

I wonder if Gido absorbed the Angel we saw in chapter 110 and whether that made him more powerful or gotten him some fragments or stigmata´s.

Gido has a lot of powers he shouldn't have, like Dean Drive and Agnischwattas, so I say its likely he did absorb a Angel and acquire all the fragments, possible except a few.