Some perennials do die back to nothing, but far more do not. They will come back next year and bloom again providing they get watered in the in between time. Just being exposed to natural rainfall or a sprinkler system is enough to get them through the year.
Those that remain green above ground are putting energy back into the root system for next year.
I fertilize my perennial beds monthly from May through September. It is just what I do in order to help them grow and produce flowers from year to year. My beds on Long Island had hostas, primrose, coneflowers, astilbe, May apple, Solomon's seal and others. They often bloomed a little better with each subsequent season.
I cut back flower stalks, but let the leaves die back and rake them up.