I really am not impressed at all yet, halo will def. stay on for 5 and 6, but destiny looks so different i really don't see a problem. At this point, i don't see it becoming the next halo at all.
Also, think of this from a marketing standpoint. The average xbox owner has no idea who bungie is, so saying Destiny by bungie doesn't help, they do that all the time with movies and who actually has been like from the director of tokyo drift?!!? gotta see that.
And activision, a smaller company than microsoft, has just a game to sell here. Yes call of duty took over halo but not until it was an established franchise.
Microsoft is a HUGE company who has a SYSTEM to sell with Halo 5. The marketing for it is going to be unreal, with name recognition, one of the worlds largest companies backing it and a 8 year development of the 720, its gonna be huge. Activision will put all their might into Destiny, but its a brand new ip, they don't have to backing microsoft has and they have time, like with call of duty or even halo, to grow the brand.
Halo 5 will have no issues selling copies.