If they've already been outside, then they'd have started getting used to the lower temperatures, so I'd be inclined to leave them out, but keep an eagle eye on weather forecasts and bring them in at night if there's any possibility of frost.

Other than that, I'd relax and leave them.

Unless there's some sort of infection that looks like it can crawl from leaf to leaf (fungus type for example) I would always leave leaves on if there's enough green area for them still to be doing useful photosynthesis. And best not to spray with anything until you're sure what it is you need to spray against. And then think twice if it's a food plant.

If you're feeling really despondent, go and buy yourself a few replacement plants just in case (or ask on Freecycle - gardeners always have either none of a plant or far too many)