It is impossible to say for certain what would have happened to Romeo and Juliet if they hadn't died, as it is a fictional story and their actions and circumstances were not based in reality. However, it is possible to speculate about the potential outcomes of their relationship.
It is unclear whether their relationship would have been sustainable over time. While their initial love for each other seemed strong, the intensity of their feelings may have dissipated over time, as is often the case with intense infatuations. Additionally, their relationship was marked by conflict and obstacles, including their family's longstanding feud and the societal barriers that stood in their way. These factors may have ultimately strained their relationship.
It is also possible that once the initial burst of passion calmed down, Romeo and Juliet may have had less to offer each other. Without the intense feelings of love and desire driving their relationship, they may have struggled to find common ground and shared interests.
It is impossible to say whether Romeo would have moved on from Juliet as quickly as he moved on from Rosaline, as this would depend on the specific circumstances and dynamics of their relationship. However, it is possible that Romeo's feelings for Juliet may have been more genuine and lasting than his feelings for Rosaline, given the depth of emotion and commitment demonstrated in his relationship with Juliet.