If Warner is elected governor in 2013, and appoints his own successor in the senate, then that appointment would last for less than a year anyway, because there'd be a special election for the seat in November 2014, correct?
Does McDonnell then decide to run for that seat in 2014, rather than waste his time on a longshot presidential bid in 2016?
No special election - term ends in 2014. I imagine McDonnell would run for the seat, rather than risking a 2016 run. Of course, it could risk a fight with Cuccinelli and Bolling.