I don't believe that is the case.
The contract had a stipulation of a right of first refusal until a certain quota of Halo sales were reached, I believe. That has transpired.
I'd say that Destiny is a bigger deal than Respawn at this point, simply because the latter is an unknown quantity -- sure, Respawn is being started by some of the leads of Infinity Ward, but that alone does not make an entire studio. Bungie on the other hand is a huge studio with boatloads of talent. And from what I've seen of Destiny, it looks to be the next big leap in multiplayer/co-op gaming for first person shooters.
We'll have to see how good Respawn's effort is.
Doesn't sound great to be honest, and after MW2, I'm not sure they have what it takes.
But then, I have little faith in Destiny.