If the sub floor is still solid--wipe with bleach and let it dry----add new 1/4 inch underlayment and reinstall the sheet goods.
That looks like OSB (flake board) if you ever tile that room you will want to add another layer of 1/2" b/c plywood on top.---Mike---
That looks like OSB (flake board) if you ever tile that room you will want to add another layer of 1/2" b/c plywood on top.---Mike---