For instance, it’s obvious Cahterine Sakai was set up to have the same fate as Sheridan’s wife. As it stands, were are left with foreshadowing in Sakai’s arc to events that eventually DID expire, but with the replacement character instead.
While it may seem obvious, it's probably not quite that simple. In the synopsis of the arc that JMS wrote prior to the first season (published in Volume 15 of the script books), we're told that around the end of season 3 or beginning of season 4, Catherine would be mind-raped and all memory of her relationship with Sinclair lost. The only way Sinclair would have been able to get her back would be by esentially doing it to her again and he couldn't bring himself to do that.
That said, whe Claudia left the show, her planned romance with Byron did get moved over to Lyta.