Multicomponent optical fibers with incorporated metals are promising photonic platforms for engineering of tailored plasmonic structures by laser micromachining or thermal processing. It has been observed that during thermal processing microfluidic phenomena lead to the formation of embedded micro- and nanostructures and spheres, thus triggering the technological motivation for their theoretical investigation, especially in the practical case of noble metal/glass composites that have not yet been investigated. Implemented microwires of gold core and glass cladding, recently studied experimentally, are considered as a reference validation platform. The Plateau-Rayleigh instability in such hybrid fibers is theoretically investigated by inducing surface tension perturbations and by comparing them to the Tomotika instability theory. The continuous-core breakup time was calculated via Finite Element Method (FEM) simulations for different temperatures and was found to be considerably higher to Tomotika’s model, while the final sphere diameter is a linear function of the initial core radius. Different sinusoidal perturbation parameters were considered, showing significant impact in the characteristics of formed spherical features. The theoretical results were in close agreement with previous experimental observations expected to assist in the understanding of the processes involved, providing insight into the engineering of fibers, both in the initial drawing process and post processing.