the possibility would still exist

[navitasan]

Tom hasn't had cancer. He might get cancer in the future. He used to smoke. And there's a history of lung cancer in his family.

1) So even if he had never smoked, the possibility of his getting lung cancer would still exist.

2) So even if he had never smoked, it would still be possible for him to get lung cancer.

3) So even if he had never smoked, it would still be possible that he would get lung cancer.

4) So even if he had never smoked, it would still be possible that he will get lung cancer.

5) So even if he had never smoked, he might still get lung cancer.

6) So even if he had never smoked, he might still have got lung cancer.

The sentences 1-6 are supposed to follow the text above them. Which of them are grammatically correct and meaningful in this context?

Gratefully,
Navi

[Alan]

All grammatical except #4.