Is it possible to travel a coastal road and avoid motorway from Dubrovnik to Split.......do you still enter Bosnia ??
Yes to both.
You can avoid Bosnia by driving to Ploce, ferry to Trpanj then drive the Peljesac Peninsula past Ston to Dubrovnik.
The motorway A1 ends by Ploce, the section to Dubrovnik has not been built yet - and God only knows when will it be