My first reaction was to think that they'd break up.. but George or Ringo don't have enough songs yet for a careers (well, maybe Ringo if he wants to do a covers album), and John is in the middle of a songwriting slump.
I think they stay together at least for one more album in 1967, then *maybe* break up in 1968 once the songwriting output ramps up again. The 1967 album may not be as big a production as OTLs Sgt Pepper is (I think Paul & George Martin steered the direction towards Beach Boys-inspired stuff), maybe more a 'garage-psychedelia', building on tracks like Rain & She Said She Said. One of John's favourite albums in the summer of 1967 was 'Safe as Milk' - the debut album by Captain Beefheart.. I can see a John-led Beatles album in 1967 being more like that.
To lay-down the basic tracks, I imagine they'd grab someone in to play bass (Klaus Voorman? John Paul Jones?), just as a 'hired hand'.. then do all the overdubs (if needed) themselves.