Rudy will lose much more than 16% of the base in the GOP. He is very likely to lose 16% or more of the entire party.
The nominee cannot afford to lose ANY of the party. It will be very difficult to pick up votes in the middle.
But he will pick up voters that are not so hard core conservative. He may even pick up democrats (i.e. Joe Lieberman democrats).
I personally know many democrats that would consider and will likely vote for Rudy, even in the Primaries because they are sick of their own party.
It may not be what the base would like to see, but it can happen that way. (IMO)