I would hazard a guess and say that the mummy they show in the teaser is an uncontrollable NPC. It's not likely we'll actually be able to play mummies.
The article mentions that you can become a mummy by sleeping in a sarcophagus. Sims can live a lot longer as a mummy, but the downside is you move much slower than a normal sim and fire is BAD for mummies.
Discoinferno anyone?