Did it look like it had dried out while you were away? Sometimes big shrubs and trees wont have rooted sufficiently while in bloom and if we go a week or so and there is no rain they can really suffer. Of course this has been a pretty damp year for us in the Hudson Valley. If it doesn’t look like it was dry it could be a disease. You might want to take a piece of it to the cooperative extension agent and have them take a look. But my bet is on it having dried out while you were away. Cleaning it up as you have and keeping it moist through the fall sounds like the best medicine at the moment. BecauseHydrangea ‘Preciosa’ blooms on old wood you will not get many flowers next year. Good luck.
It sounds like you have a Hydrangea paniculata. They bloom on new wood and so can be pruned quite hard. You can do this in the fall or the spring, though I vote for the latter. If it is growing into the walk prune that part this fall and then give it a real haircut in the spring just as new growth starts.