Rice's theorem does NOT prevent a program from giving correct answers to non-trivial properties of programs (including the halting problem or other undecidable problems) for 99.99% of inputs and "I don't know" for 0.01% of inputs. It only states that you cannot write a program that provides a correct and definitive yes-or-no for 100% of inputs.

For a decompiler, being able to decompile even 90% of programs would be awesome. We're not looking for theoretical perfectness.