There is now a TabCompleteWhitelist option in the config.yml and configuration.yml files. You can use this to specify command usages that should always tab-complete even if they contain a vanished player as an argument. This can be useful when some commands generally tab-complete all players regardless of whether they are online or not. This uses regular expressions and is intended to only be configured by developers or people who are familiar with regex. You can copy in these new config sections from the default config in the resource description.