Hosta Virus X, You have probably heard of this. I have one I am keeping my eye on. It's in a container and I will not put it in the ground. The part I don't like it that it can take years to show up!

Ahhh, but Hosta Virus X doesn't kill the plants! Often, the plants look only like they have an unusual mottling or variegation. Others will feature puckered or dimpled foliage.

If the plants are actually dying I'd suspect some root issues....perhaps nematodes or crown rot.

Here is a link that might be useful: Hosta Virus X