I don't know, they seem to be going the whole always online route so that could blow up in their face. Simulation-wise it looks really detailed though.
There is no alternative to online, given the nature of agent-based simulation. Each "resident" will have its own behavior individually simulated. Either the simulations would need to be really simplistic, or extremely powerful client computers would be required. Online simulation of complex behavior will keep the game open to large sets of users without limiting the richness of the simulation.