I'm not sure things will be as Rosie as everyone thinks for the labour party in this scenario. Heeley will be taking on the leadership of a deeply divided party and it will be obvious to all. He'd be a more effective leader than Foot, but he'd probably be forced to take on more left-wingers for his cabenet, especially if Benn is his deputy (as I expect he will be).
Come 1983 Labour do marginally better than they did in OTL, ending up with the same number of seats as they did in 1987 IOTL.
Heeley being in charge means that the left haven't necesarily been discreddited as they did in OTL and if Heeley resigns after the 1983 election (which he probably will do), his Sdeputy will be pretty keen to get his hands on the leadership. Whether this happens or not is another question, but Benn would be seen by many as the next in line.
It's entirely possible that Benn doesn't become leader of course-and whoever ends up in charge of Labour would be able to patch things up in time for a possible win in 87 and probabal victory in 1992. But if Benn becomes leader in 1983, you've probably just delayed all the trouble Foot experienced in OTL-the SDP, longest suicide note etc.