Image imported from derpibooru 
Original Description:
 
Sunny: Sobs Please survive this, dad…I can’t loose you…
 
Argyle: Everything will be okay, Sunny Bunny. If I don’t make it, look out at the stars, I will be guiding you. I will always be at your side.
 
This is my version of exactly what happened to Argyle (I’m aware it may be different in canon, it’s called an “AU” for a reason). Sunny is now 12 years old and has learned more things as she grew up, including about why Equestria fell. Equestria was threatened once more and Argyle decides to sacrifice himself to save his daughter. His intention to confront the ponies that are causing the threat, but, Hitch, Sprout, and Sunny follow him. In fact, Sunny runs to her father and sobs, not wanting to loose him. Argyle reassures her that it’s okay.
 
(I’m not going to explain because it’s a spoiler to my story, but you get to know how Sunny acquires her dad’s necklace and glasses)