You have to use storyline logic here, and there are some things you are not considering.
1) Allen is talking to what he believes to be Charline's ashes.
2) The body was so badly damaged when it was hit by the train, it was a closed coffin funeral. I believe there was a joke along the lines he exploded like a meat bag when he was hit by the train.
3) As told by Rose , the mentally imbalanced character of the show , it was quite clear they were to be married, she went shopping only to find him in the shower with another women when she came back, and the next day, he fell in front of a train.
Rose is nuts, who's to say Charlie is not locked up somewhere, where Rose can do with him as he pleases ( she has kept him drugged for days in previous episodes) and the body they found was someone else she threw in front of the train.
Yes this scenario does require some suspension of belief , but for a sitcom it is not an unreasonable , albeit a bit dark, scenario.