The plumber came on Friday and stubbed in the supplies and drain for the new sink. He also moved the toilet supply so that the toilet will be able to sit closer to the wall.
On Saturday I ripped out the rotten subfloor and was thankful the joists look fine. Just to be safe I saturated them and all the subfloor around the opening with Minwax wood hardener.
So on Sunday while Lisa and the girls were gone I put in the new subfloor down. I had some scrap 1 x 8 left so I soaked it with wood hardener too and cut it to fit in place. Since I butted them tight and the difference in true dimensional and modern lumber there was a gap of an inch and a half at the back of the opening, so of course what did I fill that space with? Leftover Oak Flooring!
The plumber will come back today to cut an opening for the toilet in the floor. My next steps will be to put down cement board and get ready to tile the floor.