After a poor opening 40 minutes the Rebels looked a completely different outfit in the second stanza with some credit due to O'Connor.
Told this week he wasn't wanted by Melbourne, the Test five-eighth came on early in the second half.
Their attack looked sharper with his presence at No.10 as they fought their way back into the game.
It was a thrilling end for Hill, who will be replaced next season by Wallabies assistant coach Tony McGahan while Test stars O'Connor and Nick Phipps, skipper Gareth Delve, Vuna and retiring prop Nic Henderson all leaving the club.
In the first half they were constantly under pressure, making too many missed tackles thanks to the Highlanders' quick ball and pushed too many passes in their own territory.
The visitors' first-half points came through tries scored by fullback Ben Smith, winger Hosea Gear, centre Tamati Ellison and then right on the buzzer by veteran prop Tony Woodcock.
But the Rebels turned the game around as Japan-bound Vuna showed the skills that made him the club's highest tryscorer with two five-pointers to get his team back to 34-19.
The points onslaught continued as English scored his second of the night and then Hegarty crossed for his first.
Fullback Jason Woodward missed that conversion that would have given his team the lead for the first time in the night and then Highlanders five-eighth Colin Slade slotted a penalty to open the gap to 37-33.
It looked like they would escape with a well-deserved win until Hegarty's game-stealing effort.
-AAP