Energy conservation is a very critical issue in energy-constrained wireless sensor networks that introduces sleep-mode related delay. Since a long time delay can be harmful for either large or small wireless sensor networks, a TDMA-based scheduling scheme has been proposed, that achieves the reduction of the end-to-end delay caused by the sleep mode operation while at the same time it maximizes the energy savings. However, the performance of this system has not been studied with respect to the topology of the network, and taking into consideration node failures. In this paper, we evaluate the TDMA-based energy conservation scheme, and compare it to the S-MAC and the adaptive listening schemes, on various random topologies. In addition, we examine the performance when node failures occur, and introduce a schedule update criterion.