Memristors are considered one of the most favorable emerging device alternatives for future memory technologies. They are attracting great attention recently, due to their high scalability and compatibility with CMOS fabrication process. Alongside their benefits, they also face reliability concerns (e.g. manufacturing variability). In this sense our work analyzes key sources of uncertainties in the operation of the memristive memory and we present an analytic approach to predict the expected lifetime distribution of a memristive crossbar.