Of course the functions of Twitter could be duplicated, and there’s nothing inherent in the coding that couldn’t be done elsewhere. What they do have, which is extremely difficult to replicate is their network in place and user base. Government agencies, corporations, and public figures all use Twitter, and some as their primary means of communication to the public. It’s not going to go away just because conservatives migrate away from that site. Institutions and public figures will need to stop using it, for it to be replaced. Even if Trump moved, it would hardly be enough.