More on the above (now is a good time to repost this); a breakdown of the collision between the two Super Giga Drills, and how if you look at it you can see this is clearly multiversal.
The two Super Giga Drills moments before they colide. Note that we see the galaxies of the Anti-Spiral dimension in the background right before they clash.
A fraction of a moment before the clash there's somewhat of a zoom in. We can still see the galaxies clearly...
And a clear shot after the first position of the clash. We don't see any of the galaxies in sight.
The first zoom out, and we don't see a single galaxy in sight.
During the second zoom out however, we very clearly see that things are different, and there are galaxies clearly visible where galaxies should have been in plain sight before (had all of this taken place in a single universe).
Just to show this, here are the two Super Giga Drills right next to each other at similar sizes (the second during the second zoom out), showing where some of the galaxies should've been clearly visible in the first.
A complete zoom out. It's here that the nearby galaxies start to be sucked in.
We once again have a zoom out, and the perspective changes again. We see more galaxies being clearly sucked in in streams (even though it's too soon for the galaxies of the last zoom out to be fully sucked in yet). I think it's safe to say that each of these streams is a universe getting sucked in to the Super Giga Drill collision...
Everything is sucked into the Super Giga Drills, even the dark blue background representing space-time; all we see are the two Super Giga Drills glowing in an infinity symbol...
Then, we see a light like a star, and the blue field of space-time returns.
Finally, right before the Anti-Spiral Super Giga Drill destroys Super Tengen Toppa Gurren Lagann's Super Giga Drill, we see the same shot as the first collision, but now there are once again galaxies floating in the Anti-Spiral dimension.
So in conclusion, the Super Giga Drills did not just destroy the Anti-Spiral dimension, as the very first clash instantly shows the Anti-Spiral dimension vanishing, but galaxies continued to get sucked in (and seen in positions that would have been clearly visible had this all taken place in a single universe). Instead it shows many universes (possibly
all universes in the Spiral Nemesis itself) being destroyed and then remade.