Bitcoin has a Lightning Network which can work independently and only uses the main blockchain to settle disputes, so it could keep operating for as long as the

Bitcoin has a Lightning Network which can work independently and only uses the main blockchain to settle disputes, so it could keep operating for as long as there was non-disputed capacity left in the isolated segment. Adding capacity would require some way of accessing the consensus, but it could be done by the parties updating their blockchain by just importing new blocks from a trusted source (not necessarily the same), like a friend with a USB drive.