Offloading is one major type of collaborations between mobile device and cloud to achieve less execution time and less energy consumption. Offloading decisions for mobile cloud collaboration involve many decision factors. One of important decision factors is the network unavailability that has not been well studied. This paper presents an offloading decision model that takes network unavailability into consideration. Network with some unavailability can be modeled as an alternating renewal process. Then, application execution time and energy consumption in both ideal network and network with some unavailability are analyzed. Based on the presented theoretical model, an application partition algorithm and a decision module are presented to produce an offloading decision that is resistant to network unavailability. Simulation results demonstrate good performance of proposed scheme, where partition algorithm is analyzed in different application and cloud scenarios.