I think Sid would have been the toughest "fit" for the post-S4 era. The Wards were written out even though it would have been easier to mold them into useful characters in the "everybody's getting rich!" era than it would have been for Richard and especially Sid. Laura was successfully molded into a useful part of this new era without losing her essential characterization, IMO, but a successful "richer" Richard might have been even more of a disaster than loser Richard. But Sid represented the very things his sister Abby seemed to hate (at least with respect to wealth accrual). In a way, Sid had to die in order to remove the one major impediment to Abby's rise to power and wealth, since his approval did mean something to her. Had Don Murray opted to stay, Sid and Abby would have had a serious falling-out over all the underhanded things she did to gain access to Gary's money and her involvement with the Wolfbridge mobsters. I think he would have been more ashamed of how she broke up Val and Gary since he would have been forced to see Val around the cul-de-sac all the time and be reminded of his sister's actions. Sid not being around to cramp Abby's style allowed her to run loose with no moral tether.
If Sid had remained and they still wanted to create a Mack-like character, he could have been Val's new love interest as long as Val could get used to all the yelling. He'd still be investigating Wolfbridge and be in proximity to all the important characters, but unlike doormat Ben I don't picture him tolerating the unresolved feelings between Val and Gary. I think they would drift apart, probably after three seasons, and he'd be paired with someone else or just leave town. KD and JVA always had really interesting chemistry onscreen and it would have been fun to see it used differently than what we got.
