I see no reason as to why he has to apologize to the fans for his own pain. He'll still promote with the members and have a blast hopefully. He'll still be loved by many. 

This was what he wrote on his Instagram

“Firstly, I’m writing this post while feeling sorry to my members, since I promised I wouldn’t write meaningful posts on social media.

“Many already know, but I’m unable to use my left leg properly because of a car accident 11 years ago.

“However, I’ve been having fun and enjoying doing activities since that time, and I’ve done so while smiling no matter how much it hurt.

“But maybe because a lot of time has passed… I’ve now become more fearful too. As I said on ‘Life Bar’ recently, my ankle pain has often become more severe.

“Sometimes people around me will joke, ‘Come on, it’s been ten years so it must be all better now!’ or ‘Aren’t you just faking it because you don’t want to dance?’ and I’d force myself to smile and move on. It’s because I’ve been doing variety shows since my debut, and in a way I’ve been living a smooth and happy life through variety… so I thought that I have to always make people laugh and act like everything is fine.

“Being a human means that even if I try to do mind control and tell myself ‘I’ll be okay’ and ‘It will get better,’ when my body doesn’t follow along, the inverse proportion with my positive thoughts makes me feel the pain even more.

“In conclusion, Super Junior is making a comeback on November 6. Since we’re making a comeback for the first time in a long while, the members and fans are all excited… and I was of course excited too.

“But I think that I will probably not be able to do normal activities. I apologize again to the fans and members who’ve waited a long time but… I really have no confidence at all [that I can]… Because I have always been thinking this in my heart, I am ashamed to face the members and fans.

“If I can make you understand and receive forgiveness with the excuse ‘I have to work hard in variety and promote!’ then I will be even more grateful as I smile and receive rehabilitation treatment, and I will try to keep my strength up.

“I finish up this post by apologizing to anyone who has possibly felt uncomfortable while reading this selfish message.

“Please don’t get a cold, and no matter how annoying it is, I ask you to always wear a seatbelt while you’re in the car.

“Thank you.”

I'm surprised Heechul is even able to walk and one can only imagine all the pain he's been through these 11 years. According to Wikipedia, Heechul fractured his left leg in five places, including his femur, knee, and ankle, requiring him to be in surgery for six hours. He also sustained other injuries, including a tear in his tongue which required stitches. The doctors have told him not to dance in danger of him injuring his leg even more.

Label SJ stated that "Kim Heechul will be taking part in Super Junior’s activities as normal"

Eunhyuk left a touching comment on his post "Hyung, let's look for a way we could be together."

Hopefully he won't overdo himself and take it easy during promotions.