Is this the end of the line for the Iraqi constitution?
It depends on the ratification process. If its only required to have a majority of Iraqis support it, then no. The Shia themselves could pass it.

However if it is being done like in the US, where every state(region) has to ratify it, then the sunni majority areas can block it.. then we have a problem.

Im not worried though, money solves a lot of problems, especially political ones.