Watched the episode again, had a few more things click into place for me.
I'm pretty sure the entire 33rd was destroyed. Right after Grace does her little jump thing, she brings up an overlay which seems to show the extent of the dimension bomb's destruction radius, along with a number of little triangles that seem to match the location of ships (multiple). We only see one, but it seems like a reasonable assumption. I'm thinking she was making sure the entire 33rd would be caught in the destruction radius before she set it off.
I think the quick flashback to the Global with its escorts at the beginning of the episode was to set a parallel with the Vajra fleet and its own escorts. I think we're supposed to draw the conclusion that the other ships in the Vajra fleet were also cannibalized from the 117th fleet (the scale is about right). If so, that's some radical modification taking place. Also, the same thing seemed to be happening to the Galaxy fleet, last we knew...
(Also, is it just me, or does the Vajra mothership sorta resemble the Birdman? What if the 117th was designed specifically to go in search of the Birdman, maybe even found it, or something like it? And then the Vajra absorbs it? Granted, a bit far-fetched.)
The rest of this I'm not as sure about, since I'm relying on the first sub, but it seems like Grace is acting to try and spark a civil war between Zentradi and humans by setting off the bomb. That seems like a pretty interesting development, if it bears out. What faction would have it in their self-interest to spark such a conflict?
The other thing the sub mentions that I found interesting is something about the Vajra following the path of the fold communications. Perhaps the Vajra are attracted to these somehow? Perhaps as a consequence of the mysterious purple crystals they seem to have assimilated?
On a final note, it seems pretty certain Grace survives, because she asks Brera to wait for further orders from her, right before setting off the bomb. She doesn't seem to be committing suicide, or just trying to spare his feelings. She's entirely in control of the situation.