I've always wondered about Bruiser Brody past '88. Incredible mind for the business, knew everything inside and out. I could possibly see him having some more matches in Japan, having a go with WCW in the early 90s before eventually retiring to a booker / agent scenario. Who knows maybe a match with Hogan in '89 or '90 in WWF!? He was a headliner no doubt.
Bret's always a fun one to think about too. Bret was always determined to stick things out, but I think if he was in a healthy capacity, he would've returned to WWF eventually for another run. Let's say Hart rides out his WCW contract that takes him to Dec. 2002. Interestingly enough, Shawn Michaels has returned and is the current World Heavyweight Champion. That's an instant program right there. Wrestlemania 19 would get even more stacked with a Hart v. Michaels match. Only fitting with Rock v Austin and McMahon v Hogan on the card as well.
So Bret signs a 5-year deal taking him to 2007, with the implication that Vince will "make things right." They keep the WH belt on Michaels from Survivor Series '02.
Jan 2003 - Entrant #27 is Bret Hart in the Royal Rumble. Wins.
Apr 2003 - challenges Michaels at WM19. becomes World Heavyweight Champion.
Aug 2003 - Loses belt in Elmination Chamber to HHH at Summerslam
Nov 2003 - Gets one on one rematch at Survivor Series vs. HHH. Loses.
Dec 2003 - Gets shipped to SD! - Works against Kurt Angle at Mania XX. Makes him tap. Becomes WWE Champion.
Aug 2004 - Has a program with The Undertaker to Summerslam. Wins.
Oct 2004 - Has a minor run vs. Eddie Guerrero to No Mercy. Wins
Nov 2004 - Has a minor run vs. JBL to Survivor Series. Wins
Jan 2005 - Starts program with John Cena for Wrestlemania 21. Loses belt.
Apr 2005 - Takes time off
Aug 2005 - Returns Summerslam as special guest referee for Hogan vs. Michaels. Screws Hulk.
Late 2005 - Hart and Hogan appear off and on, building up to a Wrestlemania 22 match. Hart wins.
Apr 2006 - More time off (entering part-time schedule)
Aug 2006 - Returns for a Summerslam program vs. Vince McMahon. wins.
Nov 2006 - Has impressive run vs. Chris Benoit for Survivor Series. DQ
Jan 2007 - Enters the Royal Rumble. Is in the final 3 with Undertaker & Shawn. Taker wins.
Apr 2007 - Battles Chris Benoit again at Wrestlemania 23 for US title. Steals the show. Benoit wins.
May 2007 - Hart enters talks for a retirement match @ Summerslam. Selects Benoit.
June 2007 - Benoit tragedy. Match is shelved.
Nov 2007 - Returns to RAW as General Manager.
Dec 2007 - Signs new 5-year deal, performing until Mania 24. After that, he gets an office / agent role.
Apr 2008 - Has final match vs. Shawn Michaels. HBK retires him.
Spends from May 2008 until Dec 2017 as road agent. Maybe a manager in some instances, like you mention. Has cushy Michael Hayes like role within the company until whenever he decides to leave, like Pat Patterson too.