Instead, at the end you have to make a choice and no matter which you choose, the game ends.
2 fixes, first is to just choose the option to help them fight. Its only 4 regular super mutants and they run down the bridge in pairs pretty spaced out. Other option for PC only, is to go into the console and spawn the 2 robot models you need. I didnt write down the commands since im playing on 360, but it should be easy to look up if you want to go that route.