Hinduism knowledge fail.
Vishnu is the maintainer. He does not could not would not FTW. his entire purpose of existence is to preserve and maintain until Shiva is ready to destroy it. Shiva is the destroyer, the magma and the FTW device.
Well, goddammit.
But aren't they both aspects of another god?
Technically. But according to hinduism ALL Gods, and as far as I can remember, all THINGS are aspects of one MEGA god who is completely beyond the comprehension of mortals. Only those who attain nirvana and similar levels on the great cycle of reincarnation can even hope to come close to knowing this being.
http://en.wikipedia.org/wiki/Hindu_views_on_monotheismthat's the hindu monotheistic view in a nut shell.
But really, all 3, Brahma, Vishnu, and Shiva are Deva's. They're jobs are to keep everything running. Shiva may be the destroyer, but he mostly destroys the truly evil things. Like the poison that was created when he lead the Deva's and Shura's in creating some magical live-forever potion on the back of the world turtle. That's one example. Without Shiva, Reincarnation would break down, and as a consequence, no one could be born again.
You get the idea. When it comes right down to it, the most prevalent sect of Hinduism believes that all gods, and possibly everything(can't remember this part) are all Brahman or Atman (different names, same basic supreme being) seen through different lens and from different views. The same way that light refracts when viewed through a prism.