When the arbiter went home he went to his home planet to fight in the war between his faction of the elites and the storm faction of elites. In the books it states that the arbiter's faction won on his home planet so the arbiter is still alive so I wouldn't be surprised if the arbiter and his faction joined the chief and the unsc to finish off the remaining storm covenant and about the flood the flood were being preserved inside the halo in combat evolved and halo 2 so that must mean that the other halos must have flood reserved and hidden inside them so they may be in halo 5. In the halo 4 terminal videos it shows that the forerunner analyzed and took DNA samples from every species and stored the DNA before they fired the halo rings so that after the rings were fired the forerunner machines could take the DNA of all the races destroyed and make clones from the DNA and send them back to their home planets to repopulate so the entire forerunner race could be in halo 5 ands its even possible that the species that created the forerunners (precursors) could be in halo 5