The prophet could have left it to fate. After all, did the Prophet not enjoy God's protection? What need was there for the Prophet to act to save himself? But we know that the Quran tells us to strive and help ourselves before Allah would help us. That is why the Prophet migrated, to try and save himself and not merely to surrender to God's will. This does not mean going against fate as whatever happens after we have made an effort is still determinad by fate.