Rhimes told Entertainment Weekly that Heigl's departure from the medical drama earlier this year tempted her to bring Izzie's story to a tragic end.
"We discussed a lot of options, and the one we settled on felt like the [best idea] without having Izzie actually there," she said. "But it also felt like the cruellest possible thing."
The Grey's Anatomy boss further remarked that she ultimately deciding against writing out the character completely because it didn't feel quite right.
She remarked: "I was ready to go, but then I went home and literally couldn't sleep. It just felt so mean. It wasn't closure; it just felt brutal. Alex (Justin Chambers) might have never recovered from it. And the audience who loved Izzie would've been devastated. So we didn't do it."
Rhimes concluded by adding that she remains "open" to Heigl returning to the show for a guest appearance in the future.
Grey's Anatomy airs on Thursdays on ABC.