I'd add to Very Old's list:
Tonny Jensen 1991 Kings and 1993 Suns
John Rillie 1996 36ers
John Dorge 1985-89 Bullets
Phil Smyth 1982 Saints
Smyth had a good debut season in 1982 but Saints lost him to Cannons, where he led them to 3 championships in the next 5 seasons. Definitely one that got away.
It's a bit of a stretch to say Robert Rose went on to better things after his first season in the NBL (1992 Magic). He won a championship in that first season and the MVP in the second season, then moved to the 36ers, Cannons, Crocs and Taipans. He did get a second MVP with the Crocs in 2000/01 but no more championships.
And what about someone like Chris Anstey? Debuted with Tigers in 1994, goes to Magic for a dfew seasons then overseas (including NBA), back to NBL with the Giants for two seasons (2000/01 & 2001/02) and then the Tigers get him back for the rest of his career. Does that count as one that got away (but they got him back again)? ;)