How risky is having sexual intercourse with someone whose ex-partner was diagnosed with HPV cervical cancer?

We don't know. What you do know is that this new sexual partner has likely been exposed to hpv strains that are the high risk type. However, it is unlikely that you or anyone else for that matter will go through life having never been exposed to hpv. Hpv is extremely common and hpv vaccine, getting regular pap smears and follow up/treatment is the only way to truly prevent cervical cancer.
Cervical cancer. Cervical cancer is not contagious. Chances are you have already been exposed to hpv, which is the risk factor for cervical cancer. Just make sure you get a yearly pap smear.