Well, the Japanese would have undoubtably sunk a large percentage of the transports, escorts, and support ships. This would have made it even more dificult for the Marines(if that’s possible) and potentially lengthened the campaign , but not necessarily so.
With FDR already showing his tendencies to alter policy decisions, and then with orders from him as Commander in Chief to find all supply/equipment necessary to support the Guadalcanal operation, my opinion is it would have turned out much as it actually did.
Don’t forget that Adm. King had already won an enlargement of the total available forces able to be diverted from the Europe 1st policy.
FDR as you well know was a “Navy” man. His political power and Navy interest is what brought about the creation of the Marine Raider Battalions, Marine Parachute Battalions, and other pro-Navy units.
Not to “oversimplify” things, or my reasoning behind my thoughts, but I think this wouldn’t necesarily have had a major impact on the Final Outcome of the campaign. I respect anyone having a diferring opinion, especially if it is an educated one that knows his history and understands it. “Tall Paul”