This isn't the "real" Spider-man. The Ultimates line of Marvel comics were essentially a complete reboot, presenting younger characters as you said, from the beginning of their stories, and then telling a whole new chronology within that new comic line. They are completely separate from the main comics that have been running for 50 years. As such, who knows, they might even stick to this death. They'll probably put someone else in the suit so that there's still a Spider-man, but Peter Parker might stay dead in the Ultimates lineup, which is much better at sticking to its consequences because it's not the main story.