  We discuss the prospect of identifying a white dwarf binary merger by
monitoring disappearance of its nearly monochromatic gravitational wave. For a
ten-year operation of the laser interferometer space antenna (LISA), the chance
probability of observing such an event is roughly estimated to be 20%. By
simply using short-term coherent signal integrations, we might determine the
merger time with an accuracy of $\sim $3-10 days. Also considering its expected
sky localizability $\sim0.1$-$ 0.01 {\rm deg^2}$, LISA might make an
interesting contribution to the multi-messenger study on a merger event.
