Hi Bill,
I can confirm that it is not necessary to have Mono.Cecil.dll present for any normal operations, and the DLLs all load correctly in standard execution contexts i.e., if you're using MEF or a DI container, the absence of the DLL as warned about will not have negative impacts.
(We intend to remove this warning as part of ongoing development work, though I cannot give a precise timeline at this point)
--Ruben