Due to the gliding range on large jets the few double engine failures have resulted in reasonable results, from the Gimli Glider to the Hudson event and more appropriately Air Transat 236 which glided onto an island in the Azores. All with no loss of life. The main point is that if it's still controllable and you keep your cool, gliding a large jet into a safe place is achievable. After all the space shuttle glided every landing and that was a controlled brick.
To add to that, all of the double engine failures on jet twins that I can think of were caused by things that made the number of engines irrelevant, like running out of fuel (AT236), or fuel contamination (BA38). The engines themselves are statistically very reliable and the chance of them failing at the same time for unrelated causes is so low it can be realistically discounted.