They may believe in some pagan god, but not the God of the Bible and surely not Jesus. They may accept a pantheistic concept of god as an impersonal force dwelling in everything but lacking the personal characteristics of a living individual. More and more frequently we must deal with people who simply don't believe Jesus would ever come to earth to judge mankind. The Bible clearly states that Jesus will come again and judge all men. Just as surely as Jesus arose, just that surely we will be judged.
Judgment is just as sure as death.
So if you believe that God exists, that Jesus arose, that your life on earth will end, and that the Bible is true, then you must believe that someday you will stand before Jesus and be judged. The Bible clearly states that all men will be present for that judgment. Every knee shall bow and every tongue shall confess. Every one of us shall give account of himself to God. In this life people often fail to keep appointments, but no one will be absent for this appointment, and no one will be tardy.