I'm sure CalBear will make my slam of this seem tame
Guadalcanal was important IOTL to show the US and Aussies and other allies that the US was a worthy combatant.
In the great scheme of things, the US wasn't hoping for much more than a draw, but they managed to sucker a large amount of IJN resources the longer they held out.
In fact, if the IJN managed to "Win" it'd be a Pyrrhic victory hanging a big "Kick Me" sign for the RAN, USN, and so forth to harass at will and dare the IJN to spend the resources tor reinforce it.
Rabaul could hold out for the whole war. Guadalcanal couldn't.
That's not to say the US Navy, Marines, and Army weren't happy to get the "W" and the experience of finding the tactics that worked against the Japanese, but it was a bloody mess even by WWII standards.
For Guadalcanal's fall to be really worrisome, you'd need the Battle of Coral Sea to be an epic IJN curb-stomp of the Allied navies and airpower which is possible but unlikely.