The fate of Paul can be seen to be linked to one of the principal themes of this excellent novel, which is the shocking brutality of war. This is something that pervades every aspect of the novel as Remarque seeks to present the brute reality of war. He thus challenged the conception of war as being romantic with its depiction as being more about savage butchery as characters struggled to survive. This of course historically is reflected in World War I and the way that new technology brought the levels of violence and carnage to terrible new levels as battles lasted for days and killing became a much more impersonal act through shelling and mustard gas.
Many critics have commented that at the end of the novel, nearly all major characters are dead, and Paul is just the final one to die. This cements Remarque's grim view of war, and perhaps there is a sense of irony in the final paragraph:
Turning him over one saw that he could not have suffered long; his face had an expression of calm, as though almost glad the end had come.
Paul's corpse seems finally happy to meet the fate that seemed inevitable for so long in the novel. In Remarque's scheme of the world, where war is so crushing and nobody can escape its malign influence and power, Paul's death is definitely inevitable.