The distant star's light and the light reflected off the planet reach us at the same time. The star's planet is a distant one like our Pluto - it takes light 5 hours to get to it's planet.
Disappearing is really different than exploding. The poll as presently presented is not answerable, either on the basis of Newtonian gravity or Relativistic gravity. Pick either disappear or explode and redisplay thread..
Well, let us say that it is no longer there. The important part pf the thought experiment is how a change affects it's distant planet - gravitationally speaking.
If we choose to imagine the star naturally exploding, and the debris moving outward in a reasonable manner for such things, it will be some long time before the redistribution of its mass has a noticeable effect on its gravitational field; its center of mass, most pointedly, will not move from where it would be if nothing unusual had happened and so a five hour interval will be much too soon to notice any different orbital behavior in the planet's motion. If we choose to imagine Scotty instantly beaming the star to another location far away, then we suddenly no longer have any mass to continue to participate in mutual gravitation with the planet. If the advanced alien civilization previously occupying the planet had voted to run the solar system on Newton gravity, then the planet, deprived of instantaneous action at a distance, will immediately follow a straight path tangent to its orbit and head for outer space. If the aliens had voted to run on Einstein gravity, with its arbitrarily chosen velocity of c for gravity propagation, it will be five hours before the planet starts moving on aforesaid tangential straight line path, as the "tail end" of the ex star's gravity reaches and passes beyond the planet.
