People have already speculated how Han may make an appearance in a flash-back, a hologram, or even as a Force ghost (the last one I personally don’t buy)
Or in a hallucination. Kylo Ren is mentally unstable.
That could actually be really interesting. It could also be a Force related thing as well, kinda like Luke’s “vision” of Vader on Dagobah. The ep. VIII script has already been described as being “weird” so it’s not impossible. If this is the case I really hope Johnson does something really dark and surreal. This is going to be the ESB of the ST after all.