Richie
The postulated conditions for considering leaving the Island were:
1. After several days and no sign of "rescuers" and 2. the plane washing off the reef after about 5 days, they realized they would either die there or make some attempt to leave the island by raft, or life boat, etc.
As Heath pointed out, and I agree with him, tis better to die trying to survive than to die just dying.
Let's see, with a steady 10 mph wind you can sail about 200 miles a day, 5 days to Fiji, 3 days to Gilberts, 4 days to the Marshalls. 20 mph and ya can cut those times in half. FN was an expert sailor, been at sea all his life.