looking good. I love the slate look. We did it in our nook a few years ago!
Do you have access to the bottom of this area? maybe you could get your hammer from below and then brace the subfloor back in. i thought i lost my favorite hammer for about 2 years... then I looked in a box of stuff I hadn't unpacked and there it was! Right next to my headlamp and my trusty leatherman I had been looking for!
That's a good idea. Now if I was 100% certain it was in there and not some other random place I forgot I left it...