Continued slab rollback will lead to continued rift settings. If the slab continue rollback (till nearly vertical), can the asthenospere upwell and produce the OIB-like rocks?
I suggest you to read some papers about the geodynamic evolution of the Tyrrhenian Sea (Central Mediterranean Sea, Italy) that is a Neogene-to-Present back-arc basin.
Here some references:
- Marani, M. P. and T. Trua, Thermal constriction and slab tearing at the origin of a superinflated spreading ridge: Marsili volcano (Tyrrhenian Sea), J. Geophys. Res., 107(B9), 2188, doi:10.1029/2001JB000285, 2002
-Zito, G., Mongelli, F., De Lorenzo, S. and Doglioni, C. (2003), Heat flow and geodynamics in the Tyrrhenian Sea. Terra Nova, 15: 425–432. doi: 10.1046/j.1365-3121.2003.00507.x