My take is that Hana could beat anyone in tennis history on any surface, if she was in the magic zone...It seemed she could do no wrong. Yet whats interesting about that series of matches was how easily Chris beat her at Wimbledon right afterward ~ when you'd think Chris would maybe have had those scores on clay & Hana the other scores on grass!
Another thought on Tracy/French Open 1979 is that Tracy was 16... never won a slam yet, and thats just a much more giant a stage to try to beat Evert on, especially if you beat her in Rome and she wants to annihilate you in front of the entire world, a habit for revenge that was her specialty. Kudos to Tracy she won the Us Open later in the year, but cant forget she was indeed the youngest ever champion. Her odds in Paris would not be too good.
Chris would have been in a good place for the Dec 1975 Aussie Open because she was in the midst of what would be an 8-match winning streak against Goolagong... if she was ever going to meet her successfully in Australia, that would be it. It was too early for Martina to trouble her and too late for Court to do so... and she'd be awfully motivated after losing that match to King at wimbledon when up 3-0 in the 3rd before Connors came in with a babe on his arm, after which Chris dropped 6 straight games... Another example where her instinct for on-court revenge would push her to remorseless levels of focus.
She was also on a major winning streak at the end of 1977, beating Wade, King, Navratilova while dropping only 1 set in 5 matches against that group ~ and with Goolagong out of the way makin' babies, she'd be a heavy favorite.
Evert did not play the Australian Open from 1975-1980. From 1975-1977 it was played in January (sometimes starting the last few days of December, but ending in January). In 1977, there were 2 Australian Opens; one ending in January, the other in December. Then from 1978 on, the event was played in November, and eventually into December, until 1987, when it moved back to January.
Here's my take on how Evert might have fared the years she didn't play:
1975 - A toss up if Evert met Goolagong in the final. (Navratilova upset Court in the QF and lost to Evonne int he finals. Morozova was also entered). Evonne had beaten Chris in the 1974 final, and beat Chris on grass at Forest Hills in September, and again indoors in the VS Finals. So I imagine Evonne had the mental edge at the time.
1976 - If Evert had played (and even if other top players did too), I believe it would have been another Chris-Evonne show. I give Chris a 55% chance of winning. Chris did beat Evonne just a week after the 1976 Australian Open, at the L'Eggs World Series 4 player exo. But that was on hard courts. And Evonne may have been tired from the post-Aussie trip. Still, Evert was playing well at the end of 1975, so I have to think she was mentally ready to beat Evonne on grass Down Under.
1977 (January) - With Evonne out due to her daughter's birth, I have to think Chris was the overwhelming favorite. Court did return for some of the pre-Aussie events. Martina won Sydney in December 1976. Even though Martina beat Chris in the first 1977 Slims event, I'm not sure Martina would have been up for toppling Chris in a major at that time. But you never know. I give Chris decent odds for winning that year. But I wouldn't argue too much if someone said Court, Navratilova, or even Fromholtz might have gotten the better of her that year.
1977 (December) - Evonne did return, and was on a tear that year. Chris had already committed to a break from the tour post-Colgate Championships. So it's somewhat doubtful Evert would have played that year. Given that she seemed a bit burned out, even had she played, this is one year I think she would not have won.
1978 - It really would have been very interesting if all the top women played Down Under that year. Many were there for the Fed Cup, and some of the warm up events. With Martina as reigning Wimbledon champ, plus Wade, Reid, Turnbull, and Fromholtz in the mix, it would have been a fun event. A toss up as to who would have won. Although I am pretty sure it would not have been Chris O'Neill.
1979 - This was the year that Evert played more tournaments and matches than any other year. Plus she got married. So I say it's doubtful Evert would have emerged victorious that year. Martina would have been the solid favorite on grass. And if Goolagong, King, Turnbull, or Fromholtz were also playing, it wouldn't surprise me if any of those players wound up winning.
1980 - A wild card year. First time many of the top the women returned, in an event played separately from the men. Martina played, but lost to Turnbull. Mandlikova won the event, as she was really starting to find her confidence. Evert would have been hard pressed to win the event. But, if Evert had burnt herself out at the end of 1980, who knows how her 1981 season would have turned out. And I bet Evert wouldn't trade her 1981 Wimbledon win over Hana for an Aussie triumph in 9180.
On balance, I say Evert would have bagged 2 more Aussie titles had she played the years between 1975-1980.