The character and world of Rocky is already set to return in Ryan Coogler's spin-off Creed, which sees Rocky training Apollo Creed's son, and though Coogler has said several times that Rocky is a supporting character, this shouldn't cast any doubt on him being a huge presence in the film. As far as continuation ideas go Rocky training Apollo Creed's son is a strong concept but it is clearly definable as a spin-off, and Rocky is Stallone's creation and there is nothing to suggest he wont see a need to continue the Rocky stand-alone films in some form. In the long-term though it has to be surmised that there will eventually be a Rocky without Stallone as Balboa - unthinkable perhaps but so was remaking Psycho... Whether or not Sly decides to make another film as a retired Rocky focussed solely on him being the trainer - which in a bizarre way would make it like a spin-off from Creed - remains to be seen. If not, when enough time has passed for the property to no longer be considered sacred it will no doubt be rebooted. A reboot wouldn't necessarily exclude Stallone, as, again, there is an opportunity for him to return in the trainer role of Mickey, though for that to happen a lot more time would need to pass, perhaps when Sly is entering the twilight of his career and hasnt been seen for a while. This would work by forging as strong a link as possible to the original, and also as a means of giving Stallone one last hurrah. And if not theyll probably remake it anyway when hes gone.