Duty cycling and energy effective techniques are employed frequently in order to prolong network lifetime in WSNs. In recent studies, dynamic duty cycle schemes are also adopted with the use of asynchronous MAC protocols. In this work, we have studied fault tolerance in multi-sink WSNs. We introduced a geographic forwarding technique in order to prevent packet loss due to node failures by employing an adaptive approach. The simulation results show that the proposed forwarder set based scheme outperforms the geographic forwarding technique with respect to throughput in the scenarios that contain node failures and gives results close to the case of no failure.