Well, Omni Man does die in the comics. The reasons behind it involve various plot developments and character interactions that shape the course of the story. It's a pivotal moment that changes the dynamics of the comic world.
Well, the death of Omni Man in the comics is a complex and intense event. It involves a series of conflicts and plot twists that lead to his ultimate fate. It's too detailed to explain briefly here. You really need to read it to get the full impact.
Not at all. The comic storylines are complex and have various factors that prevent Thanos from achieving the total eradication of everyone. There are always forces working against him and characters who find ways to survive and fight back.