I think that their network chief and their COO will be the ones actually doing the work just like they have so far. John was just the front man. If you need a CEO, Coombes has done very well at Sprint.
It has been previously discussed that the network thinning will complement either other. The best of both networks will remain. More Sprint sites than T-Mobile will be decommissioned or moved, but where Sprint is stronger (or the only one present) it will remain.