If vicehosts go missing as well, you won't be able to invite anyone in. An active host could bring in more vicehosts as well incase the current ones get too busy to set up GW and stuff.
Invite who in? The only new people on our server are guild owned alts. And they are not creating alts as fast as real people leave. We have 3 Vice hosts, so I am not fretting over any anything that happens.