If there are non seeds in the swarm and the availability is less then 1.000 then it does mean that not one complete set of all pieces is in the swarm. In that situation and when your upload ratio is much much greater then what you have downloaded you can pause that torrent and wait if a seeder comes back. But if you see seeders: 0 of 0 connected (x-thousands in swarm) it is likely that you wanted to download something that was not authorized to be downloaded and that it is a so called Faketorrent. The torrent is useless datagarbage in that case and you can delete it! (Before you ask for specifics see the global anouncement, please)