As already noted, the assumption that the alien can view our future assumes that our future is strictly classical and already determined by times that move from the infinite past to the infinite future. This is clearly an oversimplification of the real physics. If we assume that our future is not already determined for other observers (eg. since we have free will in QM) then we must figure out how another observer could see us approach a black hole event horizon and take forever to cross it. We could say that this future exists in the cosmos of the alien, but not in our cosmos. That would require either (i) that there is no experiment that the alien observer could do to view our actual future or (ii) that we never approach an horizon. Since (ii) seems too restrictive in general, the alien can only interact with us locally, through shared experience. This is more or less the standard view.
With the uncertainty of QM and QFT it is impossible for things to be preordained (even if free will is illusory). Thus the true nature of the alien's observations of us involve quantum entanglement and probably other non local features of gravity.
The idea that NOW does not exist makes no sense when we talk about quantum observers, because every measurement is NOW for the observer. Our cosmic time evolves from the Big Bang to our present. We can write down mathematics with future times, but few people believe that these realities actually exist. When we probe locality in HEP experiments, in a sense we are creating our future one moment at a time. The frontier of our knowledge is the frontier of what exists for us. This is Hegel's philosophy, if you like, which puts the NOW in a special position for an observer.