Vanilla game had some NPC and Objects whо leave island and go to the Morrowind Mainland, like this:
Vodunius Nuccius – Imperial Commoner, Player helps him to leave Seyda Neen on boat to Narsis.
Duvianus Platorius – a Census and Excise agent. He leave Vivec after player lies him that Addhiranirr get boat to the mainland. (possible he can appearance in Census and Excise Teyn Office?)
Tashpi Ashibael – escape from Vvardenfell because Ranis Athrys wants to see her dead. (can be Healer in Velothi village and under a false name)
Imperial Prison Ship – where you starts the game. (this is a lot things can do with him)
Caius Cosades – leave Vvardenfell to Cyrodiil, but according to the note from TESIV, he stayed on Morrowind Mainland.
You have plans to them?