What if, instead of Sasha, it was Martin who got killed and replaced by the Stranger in s1?
Think about it. Martin was sweet, always helpful. You couldn't say a bad word about him. He was inobtrusive and caring. But what did you actually know about him? What are his hobbies? His passions? What was his history? After all, most of the information he put in the Institute's paperwork was made up.
Imagine the Archives crew finding out the truth about him being gone and seeing that they never actually knew him, not even when he was there. That he was a replaceable figure. Good, sweet, caring Martin who never shared what was on his mind. Martin who was always so plainly kind without actually contributing much to their lives, passing by unnoticed not because he was disliked but because he wanted to. Was he ever truly there? Do you even know who the person you're mourning was? Or is it just an image of him, an image that HE created of himself and sold to you.