Free RPG Day 1 shot without the rules?

We've got a few rules to use as of this writing but not much. Free RPG Day is in a month and I'm trying to scrape together enough material to run a little intro to the system. The game would last 2-3 hours max, including the Teach of the rules (so I need to minimize that).

For these reasons I'm looking to show up with about 8 premade, level 1, characters for a party of 4 PCs. The unchosen characters would be NPCs. I plan to kill off a few characters horrifically.

I'm thinking of just narrating the collapse and doing a few rooms, basic combat, and ending in the first tutorial guild they come across.

Thoughts or ideas?