What would've happened had there been a sixth season?

Before they started filming that last season, Jaclyn Smith apparently announced that she was leaving the show at the end of Season 5 (which was the end of her contract). It's safe to assume that Cheryl Ladd would've stuck around and fulfilled her contract. And naturally, there's little chance that Tanya Roberts would've left after a single year (following the failed Shelley Hack experiment).