Hard to see why you can't make a version of this same argument, at an additional remove, in the time travel case. For example, if you are a "determinist" and / or "n-dimensionalist" about the "meta-time" concept in Eliezer's story, the future people who are lopped off the timeline still exist in the meta-timeless eternity of the "meta-timeline," just as in your comment the dead still exist in the eternity of the past.

In the (seemingly degenerate) hypothetical where you go back in time and change the future, I'm not sure why we should prefer to say that we "destroy" the "old" future, rather than simply that we disconnect it from our local universe. That might be a horrible thing to do, but then again it might not be. There's lots of at-least-conceivable stuff that is disconnected from our local universe.