The question is what does he do if he finds himself in 4th or 5th. I'd say guaranteed DNF.
Of course, If everyone does the usual p#ssypack jogfest that the USATF OT 5,000/10,000 have been reduced to, then Galen Rupp will be very comfortable two hours into a sub-maximal long run (2:10 pace) significantly slower than his ceiling marathon pace (2:05-2:06). He will easily crush anyone with him at 25 miles of a 2:10:xx race.
If anyone has the gonads to take on 2:08 pace from early on, Rupp may end up falling off the lead, hurting and alone: conditions under which he is known to DNF given his lack of racing character.
But the only people capable of that pace (Meb, Ritz, nobody else in the current weak U.S. stable) have no reason to take it on. Why risk blowing up and missing Rio when the goal for this one is top-3, not a win?
Thus, Galen either wins or DNFs with excuses. Same as 99% of his American-soil appearances.