The ideal situation for Rowbury and Simpson would be for Dibaba to make a hard push with about 500-600m to go. That will be short enough a distance for the pace still to be fast, but long enough for plenty of the people who go with Dibaba to burn out--and for Rowbury and Simpson to pick up the scraps, like Manzano in 2012 or Centro in 2011.
The key in this is for them really just to be patient--to know that it's going to happen, and to know that that first move isn't everything. With 500m, 300m, 200m to go--there's still plenty of time left in the race. Both of them have the endurance and the speed to eek a medal out of this scenario, but only if they play their cards right. What will do them in is not just trying to go with Dibaba, but making a hard, sudden acceleration at any point in the race.
More than running a fast 300 or 400 or whatever, it's this sort of hard move that tends to do runners in at the championship level. Instead, Rowbury and Simpson need to just let them go, and trust their legs to get them back.