Does a TAS of a game with no real actual credits ending count? Like for LEGO Friends, I am guessing that 100% doesn't really have an ending, and the game just will go on even after the last task in 100% is done. So would this run be automatically rejected for not having an ending if in 7 years or whatever it was submitted?
Many DS games apparently don't really have endings, or good endings at least.
This is not a problem. See http://tasvideos.org/MovieRules.html#MovieMustBeComplete. Several score-based A2600 games have the same issue you're describing, see for instance http://tasvideos.org/2599M.html, which simply ends when the high score is reached.
Your run would simply end when all objectives for 100% are completed. You shouldn't show a screen to prove this in the main submission; instead you may also provide a movie file/encode that does show the completion stats, if applicable (the shorter one would be used for publication though).
All syllogisms have three parts, therefore this is not a syllogism.