They don't need to do anything, Halo 5 isn't launching alongside Xbox*fillintherest*, perhaps another Halo product, but Halo 5 won't be ready untill November 2014 at the earliest, November 2015 most likely.

Nothing

they will just have to sit through that boost the 720 gets for 2-3 weeks before it settles down

360 had halo 3, halo reach, halo ODST, and halo 4 and it didn't stop ps3 from outselling the 360. don't think it will be a problem for them.

NextBox will have the same cycle as the 360

Since 2008 the PS3 is crushing the 360 11 months a year.
Only CoD or Halo could push it close to the PS3.
Microsoft had luck Sony screwed up so bad - The console got many hate from developers and cellar nerds(hackers).
Last year not even that could help the 360 - Halo 4 and CoD combined with the USA numbers weren't enough to overcome the lead worldwide.
NextBox will do exactly the same thing - They will have fate in those 2 franchises.
But this time Sony won't screw up - They have the love of the 3rd Party,got the new CoD with Destiny on their side and the variety in genres.Cause as it looks like a lot more people get bored with CoD and Sony will have a lot more impact directly from the start of its new console.

Sony isn't playing into the cards of Microsoft this time.
All the screw ups of Sony in this Gen weren't enough to stay on 2nd place...What do you think will happen when Sony is doing everything right as it looks like right now?Better Online Service,better games,more and better support from 3rd party and so on.

Micro can't do shiz. The best they can do is lock themself in the bathroom while Sony straps on their prosthetic legs, gets their gun, and BAM! Game over, Sony FTW, Kaz is on bail bitches! Shiz iz on steroids son!!

so.. you followed through XD

Halo 5 had a a year development?