Assuming your bottles were clean and fairly dry in the first place - then the starsan thats in them will still be good. Shake em up and the starsan will re-sanitise anything that might not have already been dead.
Pour the dregs back into your sanitiser spray bottle, its still good, why waste it.
Oh - and don't fear the foam. Starsan foam sanitises just as well as the liquid does and even if the bottle is still half full of foam - you are OK to fill it with beer right on top of the foam. As a bonus, as it floats up on the top of your beer... it re-sanitises the sides of the bottle as it goes.
Doesn't hurt the beer, doesn't effect the flavour, isn't bad for you
They are fine
Thirsty