Maybe he’ll remember Shane as a hard lesson he had to learn about what it takes to survive.
Rick could flash back to moments of Shane showing his darker side, either before the zombie apocalypse or in scenes taking place back when the characters were still on the farm.
Closure may not be a priority for Rick when it comes to Shane.
Remembering the bad times could make sense if Rick is doubting himself for keeping Negan alive; if he remembers how everything went sour with Shane, he may be inclined to go ahead and kill Negan.