No, if all peers were not reachable BitTorrent would not work at all. The reason is trivial, just study how the protocol works. Actually there are many "dead torrents" not because there are no peers with the complete file, but because those peers in the swarm are active but not reachable.
You have the impression that torrenting works even if some peers in a swarm are unreachable only because there are peers which are reachable in that swarm, so unreachable nodes (leechers) can keep leeching. This is the essence of the claims "you can keep torrenting even without remote port forwarding": yes, provided that parasites in a swarm can leech thanks to the effort of others.
Maybe you should study how the protocol works before insulting. We're momentarily locking this thread, too many off topics are making it confusing.
Kind regards