To make it clear why you would sometimes want to think about implied invisibles, suppose you're going to launch a spaceship, at nearly the speed of light, toward a faraway supercluster. By the time the spaceship gets there and sets up a colony, the universe's expansion will have accelerated too much for them to ever send a message back. Do you deem it worth the purely altruistic effort to set up this colony, for the sake of all the people who will live there and be happy? Or do you think the spaceship blips out of existence before it gets there? This could be a very real question at some point.

I don't see any difference between deciding to send the spaceship even though the colonists will be outside my lightcone when they get there, and deciding to send the spaceship even though I will be dead when they get there.

I don't think it's possible to get outside Earth's light cone by travelling less than the speed of light, is it? I'm not well-educated about such things, but I thought that leaving a light-cone was possible only during the very early stages (eg., the first several seconds) after the big bang. Of course, that was said back when people believed the universe's expansion was slowing down. But unless the universe's expansion allows things to move out of Earth's light-cone - and I suspect that allowing that possibility would allow violation of causality, because it seems it would require a perceived velocity wrt Earth past the speed of light - then the entire exercise may be moot; the notion of invisibles may be as incoherent as the atomically-identical zombies.