I did the same thing once..dropped the timing chain into the cavity when replacing it. I had the new chain hooked to the old one with the new link, and didnt think I needed to fasten it ...the end of the new chain slipped off the link and both ends of the existing chain fell into the cavity....
I am the type to use a lot of "persuasive" words when working on cars....but this time, when I saw that chain disappear, I stepped back, sat down, and sat silent for about ten minutes, thinking "is this a dream, or did I really just see what I think I saw". I managed to fish both ends out with a coat hanger, and amazingly, the loose link was still attached, and no teeth were skipped...new chain went in, and timing was perfect.

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)