Liquid-metal dealloying generates porous metals or interpenetrating-phase composites. Particularly attractive is the use of the alloy's innate melt for activating dealloying throughout the bulk, even in extended sample geometries, during reverse peritectic melting. We explore if interpenetrating-phase microstructures may be observed more generally during partial melting of solid solutions with an extended temperature interval of solid-melt coexistence. Incomplete wetting of grain boundaries by the melt is then a prerequisite for a bicontinuous structure. For a Cu-In alloy, we show that special grain boundaries remain non-wetted and provide a load-bearing backbone in the partially molten alloy, and that the bicontinuous structure is preserved during quenching to room temperature. Samples with a contiguous porosity can be obtained by leaching the solidified melt. As extended melting intervals are ubiquitous in binary alloys, our observations provide for the innate-melt-enabled preparation of monolithic interpenetrating-phase composites or porous metals in an extended set of alloy systems.