Andrew is one of the most polarizing characters in the theorizing community just by talking about him and brings a lot of emotions out in people. I'm not very interested in the one you should not have killed anymore; I’m just going to wait until something eventually comes out and adds sense. The debate has been pretty stagnant recently.   
But I do want to go over one of the potential outcomes, Andrew being it, and how he dies if he exists in the game's continuity.   
First things first, we need to establish “is game." Andrew connected to an alligator."  
The answer here, I believe, is yes.  
They’ve already kind of set up the groundwork for this.

Andrew and William's relationship seems to parallel Monty and Bonnie’s relationship.  
The alligator who hates the rabbit  
And to make things better, the secret of the mimic decided to reveal that Monty was a part of the mediocre melodies from before, as they were called the "jug band."

And the Toysnhk uses the mediocre melodies for unknown reasons to talk to Afton. If Andrew were alligator-related, and that alligator were Monty, it would make sense why he would use those characters. Monty is a part of the group.   
So we have that settled, and to make a better secret of the mimic decides to give us another advantage: the Monty springlock animatronic. I was originally going to go on the camp where Andrew died inside the Monty costume, but that doesn’t seem to be the case mainly because SOTM, none of the employees who were stuffed into the costume spring to life. Sotm is basically telling us that possession requires metal. Now we need to figure out the point where he dies, which luckily seems to be clear thanks to “return to the pit” in one of the endings before the MCI Oswald can interact with the yellow rabbit, and he’ll put a hat on him. This then makes him see a vision of finding a dead kid in the room before being killed.

Originally many people believed this was Susie; however, this is not the case actually.

1. There’s a mini game that happens before the MCI even takes place.  
2. Pittrap uses a party hat to show Oswald that the party hats are some weird form of brainwashing in the story, as in Beta's happiest day, the party keeps the MCI still, and Oswald has to take them off so they can start moving. So Pittrap is the one showing him this.   
This secret victim seems to be Andrew, which means he died before the MCI.  
Now for the final question: how could he attach himself to Afton? We know thanks to a voice line that he is at least attached to Afton during FNAF 3.

“He tried to release you. He tried to release us, but I’m not gonna let that happen. I will keep you here. I will hold you here no matter how many times they burned us." "They burn" implies that he’s referring to Fazbear Fright. So this means that Andrew has attached to FNaF 3 by the time of FNaF 3. After looking for a more concrete year, this could happen. I think I found it. It happens in 1987 in FNAF 2 during William's night shift. Let me cook.

If you listen to the Phone Guy tapes. He actually mentioned that the Freddy mask was added on your shift, Jeremy's shift; it was requested by the previous night guard. This means that William didn’t have the Freddy mask; he had to use something else to protect him during the night shift.   
I think the head he used was Monty's, possessed by Andrew, and that’s how Andrew possessed Afton. 

So TLDR for the potential Andrew timeline

. William kills Andrew before the MCI.  
He stuffs Andrew inside MCM Monty springlock, Monty possessing Andrew.  
When Afton works at FNAF 2, he uses the head of Monty to protect himself from the animatronics. This allows Andrew to attach to Afton.

How Andrew died (if he’s Canon)