Leigh made her debut as Lexie, the half-sibling of main character Meredith Grey, on the ABC series in 2007, where she had an on-off relationship with plastic surgeon Sloan until her death in a plane crash on last season's finale.
"The rollercoaster between them was always very dynamic and I think realistic," she shared to TV Guide. "When it comes to death we never know the date or the hour. There is absolute shock value to that.
"As far as their relationship, it was in some ways very young. So Rachel and Ross [from Friends]. It's so hard to put a pin in what went wrong or how it could have gone better.
"But will Mark go on? Absolutely. He'll move right along. That's just what Mark Sloane does. But initially I hope there will be a devastation."
When asked if Mark was the love of Lexie's life, Leigh answered: "I do. She learned so much from him about herself and about life in general. I do think there could have been a destiny for that."
Leight also revealed that she "didn't push" for a primetime Emmy consideration for her death scene on the season finale.
Watch a clip of Grey's Anatomy featuring Chyler Leigh and Eric Dane below: