If you look at fuel strategies from 2007-2008, even for street circuits, all drivers from 11th downwards usually filled tanks with as much fuel as possible to have a 1-stop-strategy, as opposed to 2-stoppers. Why? Because SC may not only appear on lap15, but also lap45, right before the two-stoppers window and AFTER the pitstop of single-stoppers.
It might do, but if the only chance of winning is for the SC to turn up before lap 15, then you might max your strategy for that. At the time presumably Renault were not as financially stretched as now, or as much as a team like (say) Sauber would have been at the time, for whom a safe 7th would indeed have been valuable.
And if there's going to be a shemozzle it's more likely to take place when the cars are close to each other, i.e. early. OK, a later SC would have ruined Alonso's strategy, but it didn't happen, so in that sense, which was a pure gamble, they rolled the bones and came up sevens.