How do I help my plants recover from an aphid infestation?

Aphids were allowed to feast on my window box plants while I was on vacation. My violetas were worst affected, some of which died and some look like they might be dead. Parts of other plants have also gone black.

I sprayed them with some insecticide I found at Home Depot which claims to protect my plants for 30 days. But how do I help them recover? They’re in pretty bad shape. Should I dig them all up and buy new window boxes and soil? Would new plants be ok in the current window boxes/soil?