How a major Pacific defeat could reshape the global Allied war

Which plausible Pacific defeat would prolong the Second World War most, and how?

A severe Guadalcanal reverse could have the widest effects by delaying Pacific bases, diverting Torch resources, and changing the timing of European operations and atomic use.

A Guadalcanal disaster is judged especially capable of prolonging the war because Henderson Field lay across important sea communications and lost troops and transports would take time to replace. Existing American construction would still deliver a large new fleet, potentially including Illinois and Kentucky, but reaching islands within B-29 range of Japan could be delayed. Additional demands in the Pacific could divert some resources intended for Operation Torch or affect later European operations. One proposed alternative would send part of Torch to the Pacific and land the remainder behind Eighth Army through the Red Sea. The consequences for atomic use remain uncertain because they depend on the scale of the defeat, later operations, and decisions by senior commanders. Evacuating the First Marine Division would have very different consequences from its surrender or destruction.