If $\sf RP = NP$ then the hierarchy collapses to its second level (by the Karp-Lipton theorem). But what about $\sf NP$ and $\sf coNP$?
I tried to prove that $\sf BPP$ is contained in $\sf NP$ (the other direction is trivial if $\sf RP = NP$) but to no avail, and I'm not even sure that it's true.
What do you think?