In order for Steven to live, Rose had to ultimately turn into him. The rules of this conversion have been purposely left unclear and leaves multiple fans wondering whether of not Rose Quartz will ever make a reappearance and how that would be possible. The answer itself lies in the truth behind Rebecca Sugar’s use of the mixture between reality and fiction.
Rebecca Sugar not only names her characters after real gemstones, but also allows the gems in her show to illustrate the personalities the real gems are supposed to symbolize. When considering the meanings behind these healing stones, Rose Quartzes are associated with unconditional love — which is adopted in the character by her all-consuming unconditional love for the human race. She loves them and considers their worth so high that she is willing to start a war with Home World in order to keep them alive. She also loves her unborn son so much that she is willing to lose her physical form and self enough to give life to him.
Continuing this theme of real-world-adaptation, you have to consider the fact that the placement of the character’s gems may be just as important, especially considering the fact that Rose and Steven’s gems are on their belly buttons. The belly button is a sign of fertility. It is the place from which the umbilical cord grows and attaches. It foreshadows, before Steven comes into existence, Rose’s nurturing nature as well as affinity toward motherhood. For Steven, the belly-button gem represents his connection to his mother — so why can’t it be just that?
The belly-button gem is a version of the umbilical cord. Through this gem, Steven is bound to his mother. Fans await Rose Quartz’s return, and perhaps we must first wait until Steven fully develops. The show has explained that Steven has sort of flat-lined in his aging process. He was growing for a short period, and hasn’t physically changed for years. However, his powers are still growing and changing in every season. He has gone from barely being able to summon his shield to learning to control (for the most part) his shield-summoning, bubble-forming and floating abilities. Who knows what other things he is capable of, especially when the powers seem quite infantile. Most recently, in episode “Steven vs Amethyst,” Steven’s bubble, which viewers thought was a fully developed skill, suddenly grew spikes, proving his powers to be ever evolving. Perhaps we are waiting until his powers come fully to term, and by this being so, Steven is also fully to term. In this way, like a pregnancy, Steven needs a connection to his mother in order to grow strong and fully capable when they are disconnected.
The tricky part to this theory comes when it is time for the mother and child to part and become their own people. When the child is fully developed, the mother gives birth and they are separated from one into two separate beings. This is when Rose will make her return — or debut? — to the show. When Steven’s powers have fully bloomed, the umbilical cord (gem) can be cut. But when this happens in reality, a little piece is left inside the mother and a little piece is left on the baby. These pieces heel themselves and close, but the marks forever remain. In a similar fashion, Rose and Steven will still have their gems, and continue to live as separate beings.
Steven continuously mentions the fact that everybody expects him to essentially become his mother when he's old enough - to lead them and be strong in the real way. But Rebecca Sugar specializes in teaching life lessons through her show, and the ultimate lesson left to be taught is that Steven isn't Rose. He isn't his mother and he never will be. He is his own person, and has the ability to surpass who she was and everything she did. They are not the same, and there is no better way to illustrate that than to separate them from each other and have Rose return as an individual being.