This kid was introduced in the very first chapter of this final arc, and in the first few chapters he was featured in the cover pages with Ichigo suggesting he would be prominent in the arc, but we have not seen him since chapter 500. The covers he was displayed in showed Ichigo in a mentor role towards him. Therefore, I pondered to when Shunsui told Ichigo's friends that if his power grew to great they would not let him return to the World of the Living. If this were the case, I was thinking maybe Ichigo would train him to protect Karakura Town in his stead. What do you guys think?
Indeed, however he has not been seen, nor heard of in the last few 100 or so chapters. It could be, that he was only a supporting character to advance the plot or something. Look at Makizo Aramaki, for example. He was in the rescue of Rukia Kuchiki, and now, he has not been heard of in any of the chapters.
Before this arc, Ganju Shiba had not been canonically seen (he appeared in some filler arcs) for 335 chapters. Therefore, this illustrates the point I am trying to make: just because a character has not been seen in a long time it does not mean he will never return or have no future role in the plot.
Eh. Very true. But, as long as we are debating this, I will try to disprove your points. Two of them in fact. "and in the first few chapters he was featured in the cover pages with Ichigo" I will now attempt to find all the few chapter covers that have both Ichigo and Ryunosuke. Literally, this was the only one I could find. Only this one. Also, you stated; "The covers he was displayed in showed Ichigo in a mentor role." I may be just stupid, but I don't think standing back to back would count as a student-mentor relationship.
There were actually two cover pages were Ryunosuke and Ichigo appeared together. One was this cover page at the beginning of chapter 481, but there was another one at the beginning of chapter 483 (it also appears on the back of volume 55). Here it is:
This shows Ichigo standing behind Ryunosuke urging him forward in a way similar to which "old man" Zangetsu encouraged Ichigo himself. This is the photo in particular that has lead me to believe Ichigo will become some form of mentor to him. The cover page for 481 may also signify this in some manner.