Lipid membranes are nanometer-thin soap-like films composed of molecules with hydrophilic and hydrophobic segments. To eliminate their edge energy lipid membranes form closed spherical shells or vesicles, structures that are ubiquitous and versatile, with applications in encapsulation, molecular transport, and drug delivery. Controlling vesicle topology is essential in these processes. The rapid dynamics and small scales make it challenging to study topological transitions of lipid vesicles. We develop and study fluid colloidosomes, which are micron-sized analogs of lipid vesicles assembled from rod-like particles. Their unique features enable real-time visualization of colloidosome assembly and disassembly pathways. Increasing the lateral size of a fluid two-dimensional disk-like sheet induces mechanical instability generating monodisperse permeable capsules. Closed vesicles disintegrate into open disks via an intermediate state that is topologically distinct from both the initial and final state.