That sounds very much like "Not With a Bang" by Damon Knight.
Your description is pretty much spot on.
About the only real difference is that they hadn't actually gotten all the things together. He had only just gotten the idea about doing the wedding that way. They were in a restaurant, still discussing things, when the paralysis got him in the toilet....
Except for the age of the protagonist, everything matches the beginning of the Sword of the Spirits trilogy, by John Christopher: The Prince in Waiting, Beyond the Burning Lands, and The Sword of the Spirits. They were first released in the early 1970s. They have apparently been released as a single-volume omnibus edition (as The Prince in Waiting Trilogy)...
A small robot awakes many years after a mysterious mass-extinction. Driven only by the fragmented recordings of his creator, he wanders the ruins searching for answers.
The style, story and robot seems to match. (found by searching "animation post-apocalyptic robot dinosaur" on YouTube.)
The end also ...
The post-apocalyptic setting and the scene with a man being eaten by ants (which weren't real - the torture device used in that scene created an illusion of the victim's worst fear) suggest that this could be Solarbabies, released in 1986.
The main plot concerned a group of teenagers rebelling against a government with the assistance of a glowing alien orb.