Was the credits video an after thought or can it be made to automatically play after the game?

This was handled in this post:
https://www.gog.com/forum/general/two_worlds_1_on_windows_10_pro_64_bit/page1

Download the files provided in the last but one post, and overwrite the files in your install location. The cutscenes will then play correctly.

Maybe you just missed my statement. In the video download group, there is a file at the very top that says Credits. You can play it outside the game, it shows a fly-by depiction of various places from the game. This downloaded file does not play any time during or after the finale.

Should do. If not, put a support ticket in.