Vince, the Confederates regained control of Alexandria right after it was burned and the Yankees retreated. I believe they retained control for the rest of the war. Forts Randolph and Bulow were constructed on the river there after the Red River Campaign to prevent the enemy from returning. The comment that "all is lost" in May 1865 would be in reference to the surrenders taking place at that time. Lee, Johnston, and Taylor had surrendered east of the Mississippi River and it was a forgone conclusion the Trans-Mississippi Department would soon give up, too.