They won’t reuse it in that state, but they may try to build on it. You need to fix it back into the frames with rubber bands, like this post shows:
Is your hive absolutely level? If not, they may have trouble building straight comb, and they will pick the direction that best allows them to do that.
If you had a package (loose bees and a queen with no comb or brood), you probably won’t need to treat right away, because you will have a natural “brood gap” while they build comb, stores and queen finally starts laying. I would let them get established first, because even oxalic acid is hard on the bees.