At the wedding of Riza Hawkeye and Roy Mustang, a man arrived late. Instead of quietly entering, he opened the doors as wide as he could and stood in the doorway.
With a giant grin on his face, he greeted them and told everyone that he couldn't miss this for anything and walked over by his wife and daughter while everyone else watched him open-mouthed. The man was Maes Hughes.
After the wedding, Roy asked him to explain to him and everybody else how he came back. Maes picked up the microphone and started talking.
He knew he would die if he continued his research. So, with some help, he paid a visit to Death. As it turned out, Death supported Royai too and would have liked almost nothing more than to see them get married. So Maes made a deal with Death.
If Roy and Riza got married and he had been killed prior, Death would allow Maes to return to Amestris alive because he was Roy's best friend and would hate to miss such a wonderful event. Death told him that he would think it over.
Maes went back home with confidence, but no clear answer. He continued his research, and just like he predicted, he was killed. Death had still not decided, so he let Maes stay in front of the gate (like Alphonse's body).
So when Roy and Riza got engaged, Death was in the best mood he had ever been in. Taking advantage of his giddiness, Maes finally convinced Death to let him go.
Instead of appearing immediately, he first went to Xing where he lived with Ling and Lan Fan until the wedding.
After the wedding, he went back to live with Gracia and Elicia, was reinstated into the military where he found out that he was a Brigadier General and is now spending his time visiting every house in Central to show them pictures of Gracia and Elicia and teaming up with Denny Brosh's siblings in pressuring him to ask Maria Ross out.