Let them invest to compete, instead of merging. Merging will only make things worse.
If they don’t, Sprint tanks, and we still have three main market leaders, however two will remain significantly ahead of the third. Keeping in mind that the two that are ahead are now playing the monopoly game and buying into other industries (see AT&T and Time Warner or AT&T and DirecTV or Verizon and Yahoo, etc)
Approve or not approve, regulators are sometimes forced into a position of "picking winners" :-(
Another thing that needs thinking through is what happens to Sprint's spectrum if the company goes under. What kind of rules will be placed on that auction? Would ATT and Verizon be likely winners of such an auction?