Thermoreversible, supramolecular self-assembly in multiblock copolymer melts is investigated with two microscopic approaches. We consider a blend consisting of two chemically distinct, but reactive homopolymers. One homopolymer has a single reactive end group at one of its ends, while the second has functional end groups at both ends. Reversible bonding is constrained to occur between dissimilar blocks so that this mixture is capable of forming diblocks and triblocks but no other copolymers. All copolymer concentrations are thus controlled by the bonding strength, segmental incompatibility, and the relative proportions and chain lengths of the homopolymers. Changing the ratio of homopolymer chain lengths, which controls the architecture of the copolymers, has a dramatic effect on not only the extent of reversible bonding but also on the phase morphology, which is reflected in the equilibrium mesophase structures and liquidus line. Two characteristic mean-field (SCFT) phase diagrams are calculated at high bonding strength to illustrate this architectural dependence. The high-bonding strength phase behavior is explained with a mean-field analysis of the copolymer densities. Trends in the phase diagram for the weaker bonding regime, which include reentrant behavior, are investigated using the random phase approximation.