“It’s definitely not a clip show, it’s definitely ... was to all of these people. NCIS’ tribute to David McCallum and Donald “Ducky” Mallard will air tonight at 9 p.m. ET/PT on CBS.

So that's exactly what the episode did - show old ... He left NCIS in 2016. The episode ended with a title card that read, "In memory of our dear friend and colleague David McCallum.