The three biggest "what if's" in my opinion are:
1. What if the Oilers stayed together until 1995? Gretzky, Messier, Coffey, Kurri, Anderson, Lowe, Fuhr were all still very good at that point. That would have given that core another 7 years together, and maybe another 3-4 Cups. Without Coffey on the Pens, I wonder if they would have been able to beat the Oil Machine in 90 and 91.
2. What if Bobby Orr was healthy and played a full career? He already won 8 straight Norris' and some Art Rosses. If Bobby was healthy, he could have easily won 10-12 Norris Trophies, more hardware, and easily established himself as the clear, undisputed GOAT. Some already consider him the GOAT and he was robbed of 7-8 prime years.
3. What if Henderson never scored and the Soviet Union won the 1972 Summit Series? Does this change the program in Canada for better or worse? Does this somehow expedite the Soviet players release and ability to play in the NHL?
4. What if Lindros was winning to go to Quebec? With a core of Lindros, Sakic, Sundin, Nolan, Kamensky, etc. do the Nords win a Cup? Do they somehow stay in Quebec?
As for the others... "Lemieux's health", "Crosby's health" etc. ... we all kind of know how it would turn out. Both players played long enough and accomplished enough to paint a full picture. Orr was the one who was robbed of the majority of a decade.