Ali was no longer prime by 1978 and was already pushing it in the Leon Spinks fights which went 1-1, his last victory making him the first fighter to win the heavyweight title thrice. He went into retirement later that same year no longer motivated at continuing on pro boxing. After a quiet retirement through the whole of 1979 and first half of 1980, he made an ill-advised comeback and challenged then champion Larry Holmes and lost by retirement in the tenth round. He would have another fight before finally hanging his gloves for keeps against budding contender Trevor Berbick and lose by UD.

Given those background, I don't think Ali would be motivated enough to come back from retirement in 1979 to face a relatively less famous South African fighter Gerry Coetzee whose only claim to fame by that time was his first round TKO of the same Leon Spinks whom Ali virtually toyed with just a year back.

Assuming for the sake of discussion that Ali indeed was moved enough to stage a comeback, I think Ali would still have enough of his skills and smarts left to deal with the still relatively green Coetzee.

As things really went that year, Coetzee dropped a one sided decision to another young horn John Tate for the WBA heavyweight title which Ali himself vacated in his retirement.

That is another reason why I think Ali would not come out of retirement. Ali would not come back only to fight for a share of the universal title he once held and against a then relatively obscure foe as Coetzee.

P.S. I learned recently in the internet that in 1980, Ali was motivated enough to come back for a fight against Big John Tate, who had beaten Coetzee for the WBA title but Tate was unfortunately upset by Mike Weaver hence Ali opted for Holmes who had by then won the WBC crown against Kenny Norton.

If he was in shape Ali would beat Coetzee easily. they were not in the same class of boxers.

Ali by stoppage

ALI