Indeed, drive imaging and cloning is a must. When it comes to sessions, if it doesn't exist in 3 places, its not backed up(and one of the 3 places should be in another building or at least at the other end of the house)
Maybe grab another big external drive, save copies to it and then store it in a small fireproof box(better to have it and not need it, than to need it and not have it)