I don't think there should really be any concerns as far as competition, since satellite competes with many cable companies as well as OTA and broadband options for some people (depending on their viewing habits)
While it is true that there are some people for whom satellite is the only option, that's not really a problem because there isn't discriminatory pricing of satellite depending on where you live, as there is for cable. As an example, where I live there is only one cable company. A slightly larger city a half hour to the north has the same cable company, plus a second one. My cable company's prices are about $15 less per month for the same exact package in the other city, because they have competition and we do not.
Satellite doesn't work that way, a Directv subscriber in the middle of nowhere who has no cable or broadband option pays the same for Directv as someone in a big city who has four cable companies and a ton of broadband choices. All subscribers pay the same price nationwide, based on their package, other than a few dollars more in areas that have a lot of RSNs.
If Directv and Dish merged and then tried to raise prices because there was now no competition for "satellite TV", they'd lose a lot of subscribers in the areas where people have many options. The money that would cost them would far outweigh them being able to make more money from the people who have no or only one alternative - and obviously even they all have some point where they'd go without TV entirely if the price was increased too much.
Buying out Dish would allow Directv to either become more profitable while still charging the same prices, or become more profitable by lowering prices and adding even more subscribers. Satellites aren't cheap, but you need the same number of satellites whether you have 1 million subscribers or 100 million, so the more subscribers the better so the 'per subscriber' cost of building/launching/operating the satellites is reduced.
Obviously they'd be stuck with the cost of operating both satellite fleets for a while, since they can't switch everyone over to Directv overnight. It would take several years at a minimum. But they'd never need to launch any new satellites for the Dish subscribers, and if the Dish Network satellites still had some useful life left after they switched everyone over to Directv, they could be sold/rented to others similar to what they did with the old 72.5* satellite that Russia is leasing.