this happened to me in Pencil2D a while back where i lost half of an episode i was working on and i was so freaking pissed because i was at the background stage and was just about to export.
THANK GOD i had a version with just the lineart and colour saved in Discord (because i was trying to show off) and while i lost all the shading and had to colour all the white spots in the frames with pink so i could at least edit the backgrounds in; it taught me to always' save as' instead and kill my storage

That was good

A good story here real life experiences seem to come alive much better on flash animation, but you did a really good job re doing this and was pretty amazing so nice work here, I love the story and the ending was perfect verywell done animation you have here, you should make more like this.

~~THINGS TO IMPROVE ON~~
just make more.

~X~

I had a very similar thing happen to me and one of my drawings I was working on for a while. I was finally finishing putting in all the permanent lines over the sketch lines, when out of nowhere, my laptop froze and became unresponsive. I force restarted it, but it never booted back up. Had to buy a new hard drive and lost all that progress. I know how that feels...very good work, though, bud.

Pro tip:

Save your source files on Dropbox. Revert to previous versions.

Stage 4 is the hardest one. Funny animation, I guess this relates to a lot of things: not just your Flash program crashing but maybe also a game crashing without you having saved the game. It might have been funny if you made the animation into a loop instead of ending it (again) at the beginning.