Oh my god, i honestly would've found some humor in them going futurama style with Pablo's head in the future setting and ash having to carry him around or their just bantering back and forth. Though this was probably just a spit balling idea with rob and the writers probably wasn't concrete. I'd imagine they were going to have this lead to them putting his head on a android body for him to use, now that would've been dope.
Going to elaborate more on this, i'm thinking just piecing together what i can gleam from the concept arts that have been shown from s4 and what they mean including the tid bits of info that's now been revealed from ray here, i'm gonna say Ash arrives at the base, Pablo is completely fine sporting a new look for the apocalypse and showing Ash around plus getting him up to speed, a invasion of the base happens later on during the season, Pablo is a casualty among the chaos and his head is preserved and is attached to one of android bodies he helped build.