Yes the excited states might decay by other channels. But internal conversion is a relatively slow process compared to gamma decay. It is extemely improbable that internal conversion like processes can suppress gamma emission in every case. We need to look for different explanations for the absence of gammas. The obvious candidate is fragmentation.
I'm 100 percent for fragmentation — my assumption is that fragmentation, or fragmentation together with alpha decay, produce heat in the first order when they are present, and everything else is a secondary process in such cases (although not every case).
I would not rule out something akin to IC for secondary channels, though. The following assumptions might be sufficient: excited states are produced only rarely by the first-order process; the underlying mechanism that drives everything is a transient spike in electron charge, which, when the spike happens, saturates the local region with a huge amount of negative charge which produces an IC cross section orders of magnitude larger than it would be in the equilibrium case; it is precisely and only under such conditions that the IC-like process overwhelms other channels. Now we have secondary processes producing excited states with significant attenuation through something IC-like. Not no gammas, but not gammas commensurate with excess heat. But perhaps gammas correlated with excess heat.
My understanding is that in regular fission, the daughters are often left in an excited state; or is this wrong?
I think this is correct. Heavy isotopes have far more excited states than light isotopes. We know that the neutrons emitted from actinide fission have energies of only a few MeV typical of the energies of excited states. This suggests that fission creates 2 excited daughters which successively decay by neutron emission and then by beta emission. In fact it is impossible to model a neavy fission process in which neutron emission were simultaneous with fission.
