I'm curious as to if there is some combination of a fusion and fission event simultaneously occuring that would only produce 56 nucleon number nuclides. Such that the net energy out of the fusion reaction is equal to the activation energy of the fission one.
In theory this could happen provided the correct conditions would hold. But in reality fission will yield fragments most probably having 2/5 and 3/5 of the mass of the original fragment, and some 2 or 3 neutrons will take part of the kinetic energy. So that already imposes that the medium needs to be in some heated state so that nuclei have the required kinetic energy that would allow them to interact with the fission 56-nucleon product to yield back the original heavy nuclei, but missing 2 or 3 neutrons now, which would make it beta-unstable. You can also see that for 235U, for example, already the probability of yielding a 65-nucleon fragment is rater small, since the more probable 2/5 fragment would have around 90 nucleons, which 30 nucleons more, so a fragment of 65-nucleons although possible, is rather less probable.