It depends on whether or not Disney still views the series as vital. But yeah, Sora won't be let go of entirely. Maybe the successor to the series will be him re-establishing the Keyblade Order alongside the other wielders (i.e. Kairi, Lea, Riku, Micky, Aqua, Ven and Terra) and taking on apprentices or maybe his offspring will play a pivotal role from there on out. Or they don't bench him entirely, given that, you know, he is only 16 or 17 in KH III? I actually would want Nomura to sort out the mythology a bit after III.