There's a subscenario of c.ii that I think is worth considering: there turns out to be some good theoretical reason why even an AGI with access to and full-stack understanding of its own source code cannot FOOM - a limit of some sort on the rate of self-improvement. (Or is this already covered by D?)
In this subscenario, does the AGI eventually become superintelligent? If so, don't we still need a reason why it doesn't disassemble humans at that point, which might be A, B, C or D?
Suppose we could look into the future of our Everett branch and pick out those sub-branches in which humanity and/or human/moral values have survived past the Singularity in some form. What would we see if we then went backwards in time and look at how that happened? Here's an attempt to answer that question, or in other words to enumerate the not completely disastrous Singularity scenarios that seem to have non-negligible probability. Note that the question I'm asking here is distinct from "In what direction should we try to nudge the future?" (which I think logically ought to come second).
Sorry if this is too cryptic or compressed. I'm writing this mostly for my own future reference, but perhaps it could be expanded more if there is interest. And of course I'd welcome any scenarios that may be missing from this list.