Month by month, it increasingly looks like it could be a matter of time before the two-star Marine headquarters in southwestern Afghanistan ceases to exist. Regional Command-Southwest, as it is known, was established in 2010 as the U.S. rapidly expanded military operations in Afghanistan, surging thousands of troops there. The Marine Corps was among the first involved in that surge, seeing its footprint grow in Helmand province from about 11,000 in 2009 to 20,000 the following summer. Maj. Gen. Richard Mills took command that spring of the newly formed RC-Southwest, which split off from the neighboring two star-headquarters in Kandahar…