Unless there is a real serious permanent injury, maybe like Graf in the late 90´s, I think it´s still realistic to think there´s a small little chance for a comeback. The comeback itself and her last disapointing seasons are no big excuses, this would be a different tour and succesful comebacks are possible, the main problem I think would be age and motivation, they´re not too old to play but maybe too old to make a combeback after so long, but in this messy tour, their skills and consistence could be gold worth
at the same time both of them did come back and would not want to do it a second time.
Clijsters after having a child too, winning 3 slams (2 USO, 1 AO) on return.
Henin also had a decent comeback making the AO F immediately, even though she couldn't win a slam then.
So for the two of them they did enjoy time back in the sport and have absolutely no regrets having closed on such an amazing chapter of their lives. Clijsters is a proud mother and wife, same with Henin.
I would love Li Na to come back but that would be selfish of me. Li has done remarkable things in the later stage of her career and I would not have her suffer physically just to see her back in action. She is also a proud mother and wife. One day this will happen to everybody's favourites. We just need to savour the moments they provide for us.
I will point out that it is quite possible to keep playing well north of 35. Kimiko Date-Krumm's return is proof of that. Amazing how she's played to two very distinct eras, having faced Graf-Seles-Sanchez-Sabatini and then come back to play the William sisters and contemporary players. I think her days are coming to a close soon but she's enjoyed her time back, but few would want to.