If the leaves suddenly wilt, brown and die on a hosta in mid-summer, tug on them and see if they are rotted right where they join the crown. If they are, take a look at that bud. If it is dry or deformed, chances are pretty good you are looking at southern blight.
It is a fungal disease (Sclerotium rolfsii) that can affect hundreds of plant species and it can reside in the soil. So remove any suspect hosta and destroy it.