Water leaked from second floor to first (ground) floor. What should I do / be worried about?
At this point, I would make sure all the leaks are fixed. I would put fans in the bath to circulate air and help dry things out, possibly 1 downstairs where you drilled the hole, if everything drys out without the floor swelling or the wall board coming down or warping in a couple weeks patch the drilled hole and repaint as needed or replace the wall board if it sags. Over the years I have made quite a few repairs like this, if the water was not dripping for a long time and drys quickly I would not be worried about mold.