If the statute above is current, then yes Napolitano would have to appoint a Republican (yes she could appoint a RINO)...
but yes if McCain resigned upon securing the nomination, then presumably the office could be filled in November.
The filing deadline in Arizona for the September 2, 2008 primary is June 4. The governor might have some additional wiggle room beforehand. The Idaho primary is May 27. If McCain resigned on May 28 I would think the governor would probably still schedule the primary.
There are only 3 other contests that McCain would have to compensate for:
June 3 New Mexico R Primary
June 3 South Dakota D&R Primary
June 28 Nebraska R State Convention
If McCain does clinch on or before May 28, I would recommend that he resign. It will help him get a more favorable vote in the Senate, should he win the Presidency. It would also free up time for him to concentrate on winning the Presidency.
Good work on the filing deadlines and primary dates. However, I don’t think that AZ would be bound by the current filing deadline and primary date for the special Senate election-—they could set a special primary for October or, even if they leave it for September (which would be the least costly thing to do), I think they could have a July filing deadline for such special primary.