If you recall, Dr. Jenning as the Dark Lord tells Bev that the dark lords cannot live on Earth unless they grow inside of a human body. That's why he kidnaps Bev in the first place. Soooo...all they had to do was just say, "Hey, let's grab a cup of Coffee, I think Jenning could really use one..." , walk away and the dark lords would die as soon as they touched ground. The laser would still be intact and Howard could go home.
Plus, those dark lords weren't all that powerful. The first one blew up within a few seconds of being shot. There were how many in the vortex, like 3 or 4? C'mon, just use your neutron disintegrator and blast them to pieces.
Oh and did I mention that this film ROCKS!