It is hard to say. They might consider you AWOL if you don't get back on the ship. Plus, why would you want to 1) pay for a hotel, 2) pay for dinner, and 3) pay to drop a rental car in Hilo (usually at least a $30 surcharge if not more). It will be dark when the ship leaves Kona (close to it) so what is there to do, anyway? If you like the Big Island, plan a longer stay there next time. Just a thought...
Unless the Infinity has the pass card system like they have on Princess (ie, ID cruise card that you need to put in the computer machine every time you board/disembark) then I would think you could s-n-e-a-k off in one port and travel over land and just go meet the ship the next day at the next port. There is no way for them to otherwise know you are not there.
In Bermuda on the Horizon I went from one port (King's Wharf) to another (Hamilton) in one day and the ship travelled it independently of me, but that was all in the same day!
"other than your cabin steward, who will miss you???"
And if your cabin steward reports that you are missing have you considered what might happen? Perhaps they will think you fell overboard during the night and will institute some sort of a search or even alert island authorities. If you are thinking of spending the night on the island and meeting the ship at its next port on the other side of the island, check to make sure it is permissable and, if so, be sure to notify ship officials so that there is no chance of creating a problem.
During the 13 hours of travel you should be sleeping during some of the time. I rented a car in each port and plan to explore half of the island each day. The money you save for the hotel and food will more than pay for the car. As long as you have your boarding pass they will let you back on board in Hilo.