Looks like I'm going to have to read Vulcan's Heart for starters, then the SNW story. I am thinking that if they were repatriated, it was probably through an intermediary and thus kept the Romulans and the Federation from talking or meeting directly in accordance with what was presented in "The Neutral Zone".
Charvanek probably found some old freighter, gave it to the Ent-C survivors, and gave them clearance codes out of Romulan space while wishing them well.
As for Tasha - like I said, she was under the control of General Volskiar and so there would probably be nothing Charvanek could do for her. Volskiar was too well connected.