Re-inviting someone who accidentally left a group conversation

[sweetsunray]

With several posters we are talking about re-reads per PM. Someone accidentally "left the conversation" by deleting the group PM, and now I cannot seem to be able to invite them in again. I can re-invite someone I removed per request, but not someone who left themselves. I've tried tagging too, but that doesn't work. Is there any way to solve this, without having to start a complete new PM, since we do not want to have 2 conversations going nor lose what we talked about?