In addition:
Torrent's for private trackers, like GayTorrent.ru's, have the "private" flag set. Some call that a Digital Rights Restriction (DRM), because if a torrent client respects that flag, all good do, it allows only peers from the tracker. That means only peers which are members of GayTorrent.ru and have a valid passkey can get the IPs of other peers.
In opposite to that, public tracker torrents, like those indexed on The Pirate Bay or KickassTorrents, don't have that flag set and the client can get peers through other mechanism like DHT (Distributed Hash Table), PEX (Peer Exchange) and Local Peer Discovery.
So once the tracker isn't up and running, or the torrent removed ("unregistered torrent"), the clients will no longer get IPs of peers from the tracker. As long as the peers already known by the client continue to run the torrent, the exchange of the file can continue. Some clients like µTorrent don't save the peers information when shut down, others like qBittorrnt do, but as IPs are often given dynamically or peers seeing the torrent turning "red" stop it, exchange will stop sooner or later.