Judging by the awesome attitude and service we've all received from the Honolulu SC from Luke and his team, I'm sure they would jump on a plane with their tools as soon as possible for any Kauai owners. Fortunately, as I'm sure many here will attest, the need for service is very minimal. The only time I visited the SC after almost a year of ownership was to get my tires rotated and the titanium shield installed.
I wouldn't be surprised if, by some chance you had a major problem, you could get them to authorize a rental car for you to use until they could get over with the appropriate parts and techs to fix it.
And yes, it's unfortunate that the Superferry was killed. Ironically, the folks in Kauai contributed in part to its demise.