Trump will win IA, NH, SC and NV, and then steamroll FL.
Even if your scenario with the birther issue were true, the other issue isn't going away. That's the Goldman Sachs low-interest loan. That in combination with Cruz's previous support of increased H1B visas and his strong support of the first TAP is just too much. The Cruz narrative is crumbling.
Also, it would be easier for Trump, if he wins the nomination, to ask for and get either a declarative judgment or a Congressional resolution, or both, completely erasing the Cruz birther issue.
I see a Trump/Cruz ticket forming in the distance.
Whether Trump wins the nomination or not, his presence in the race makes it possible for a conservative to be nominated this time around, I still expect the RNC to pull some wires and try to nominate their preferred gope no matter what happens in the primaries.