Jesus said that he is the true vine, and we are the branches. When a Christian (one branch) dies physically and is taken up into heaven (he might have to go through purgatory first, of course), he isn’t broken off the vine. He remains in Christ (Rom 8:38-39). The deceased Christian is still united with the vine (Jesus) and with the other branches (all other Christians, living or dead). This communion of saints makes possible the sharing spiritual things with other Christians—including intercessory prayer.