Wireless sensor networks (WSN) are composed of battery-driven communication entities performing multiple, usually different tasks. In order to complete a given task, all sensor nodes, which are deployed in an ad-hoc fashion, have to collaborate by exchanging and forwarding measurement data. We define the behavior of the overall sensor network based on the parameters lifetime and functional density. The functional density describes the distribution of all necessary tasks in a given geographical area. The lifetime is primarily given by the time each task is successfully performed by at least one node, i.e. the functional density of all necessary tasks. Nodes can become unavailable due to insufficient remaining energy. We assume that sensor nodes can be reconfigured or reprogrammed by a mobile robot system. There are various reasons for considering robots for this reconfiguration, e.g. reliability, security, and deployment issues. In this paper, we evaluate the advantages of exploiting reconfiguration and reprogramming schemes WSN using mobile robots. The primary objective is to increase the lifetime of the overall network. This goal is achieved by optimizing the functional density of heterogeneous tasks. Based on a developed simulation model, we discuss the advantages and performance characteristics.