If you look at the maps of the Mauna Loa rift zones in post #27 by
@lynne , you can see the main risk would be toward Hilo, and maybe to the southwest toward South Point if the SW rift zone were to activate (which isn't expected). Anyone traveling to Kohala/Waikoloa should have no issues, other than maybe an increase in Vog. The only other impact might be if the flows were to eventually reach the Saddle Road between Kohala and Hilo, it would mean that shortcut to/from Hilo would be severed for a while, requiring the long drive around the south tip or around the northeast coast that we all had to do before Saddle Road was improved years ago.
If I were traveling to Waikoloa tomorrow, there's no way I would even contemplate a change. While it's correct the risk is non-zero, there's also always the risk a major earthquake somewhere in the Pacific rim could generate a tsunami on Hawaii with no warning. I would expect the risk of this eruption requiring an evacuation of Waikoloa to be in the same probability category as a major tsunami - not zero, but very, very, very low.
Waikoloa would have more to be concerned about if Hualalai were to erupt one day. I believe it is still considered active, even though it has not erupted in over 200 years.