With Vitali for a while, but Wlad would box circles around him after the 4th round and stop him around 6.
Chisora is a huge puncher. So yeah he has a chance against everyone. I think Helenious was rocked a few times. I have seen Chisora KO numerous fighters on the British circuit ala Danny Williams, Carl Baker and Sam Sexton. He proved he can punch.
Helenius is a big guy with power and chin, but he doesn't have the punch output, movement, accuracy, ring generalship or experience of the Klitschkos. Most importantly movement. Wlad and Vitali aren't going to stand there letting Chisora tee off on them. So sorry Koman. Chisora isn't the saviour you are looking for