When we started using the tool we had defined several "lists", and were not using segments properly. I've now compiled one list, comprised of all subscribers from all the various lists and created relevant segments, so all is now as it should be.
However, we have sent campaigns to these these old lists and related segments, so if I delete the lists (they won't be used any more and are just clogging things up and confusing us), what happens to the old campaigns, and more importantly visibility of who these were sent to, and the related activity? Is that history lost with the list?
The campaigns and all campaign reports will still exists, so you'll still know who they were sent to, what they did, etc. The lists though and any subscriber history contained in those lists will disappear when you delete the lists. The subscribers themselves won't be suppressed and you'll be able to add them to new lists, but their previous history will be gone with the old list. The subscriber history is list specific, so it doesn't travel from list to list.
Hope that helps!