if its the P0420 code then yes it'll need a converter, but if the EGR port is clogged (P0401 EGR airflow insufficient) it can/will kick O2 slow response codes(P0133 or P0139) that will effect the converter over time if nothing is done, If there is a code P0401 I'd get that port unclogged, then drive it around to see if the other codes go away, but remember if there's a P0420 then the converter will need replaced
I've seen dumbass's here at the dealership replace the O2 sensor because of the slow response code and not fix the problem because it all comes back to the EGR port being blocked with carbon build up creating the real issue