The network lifetime measures for wireless sensor networks are mostly based on the percentage of live sensors. However, the lifetime definition must be in accordance with the primary functionality of the network. In surveillance applications, the network must be regarded as dead if the required security level cannot be provisioned. In this paper, we analyze the temporal resilience of deployment quality in surveillance wireless sensor networks and propose several lifetime definitions. It is concluded that having just the necessary number of sensors to satisfy the initial deployment quality requirement is the best strategy to favor the network lifetime.