“The Last Zeppelin”
As the destruction of the alternate universe continued (after Peter activated the Machine), eventually there were very few people left alive. Walternate realized he would have to somehow cross over and beg the other side for a truce. There was no possible way to do this except try and get through the major rift that had appeared in the sky over Manhatan. The Secretary and a heroic crew of four or five pilots took the last undamaged zeppelin on a desperate journey into the breach. By sheer chance, only the Secretary made it through alive. This was the last thing that anyone in Manhatan ever saw.
So, later that day, amazed people in New York harbor witnessed a flaming Zeppelin coming from Over There before it crashed into the ocean. Awesome. Sad, but awesome.