Potato Blackleg

The original seed potato usually (but not quite always) turns to mush - the rather unappealing looking spud sitting on a length of wood in one of your pics doesn't look like it's been suffering from eelworm - nothing else looks at all unusual to me for a spud plant looking for a seriously good 'rest' having done its job.

As for potato leaves, being closely related to tomatoes their main purpose in life is to keep forums like this in business - they often look as if they are signalling that something really awful is about to happen (sometimes it does of course, but mostly it doesn't!  )