Siddharth Nigam was approached by the makers for KKK12, however, he had some prior commitments. And hence, he couldn't take-up Khatron Ke Khiladi 12. However, he is all game for the next season.
Divya Agarwal, due to prior commitments, Divya couldn't be a part of Khatron Ke Khiladi 12.
Dipika Kakar and Shoaib Ibrahim were approached for Khatron Ke Khiladi 12 too. However, reports state that the two weren't ready for such a show right now. There has been no confirmation whether they were approached or not.
Urfi Javed was also approached for Khatron Ke Khiladi 12. However, the viral sensation, reportedly, said that she wouldn't risk her life like that.
Kunal Jaisingh said he would want to be a part of it but in the near future