Better Off Forgotten...
He came back, just like he said he would. After the battle with Knives. Trouble still followed him around like that odd black cat, but the damage was substantially less. That being said, Meryl and Milly were naturally called back to headquarters.
Both declined. They wanted to stay with Vash, and help him with Knives. Together they lived peacefully, for the most part. It was the life Vash had always wanted. The life Rem would have wanted for him.
No matter what though, Vash still wore that old red coat. Meryl took to asking him about it. When she thought back to the months she and Milly had spent searching for him, the one constant-the only constant-to the wild rumors was his red coat.
Then one day he finally told her. Told her all about Project Seeds, and Plants and Rem.
Rem....
He told her everything about Rem, and how similar they were.
The next day, her bed was found empty, her bags packed. The note only said, "Bye Vash, Sorry Milly." Meryl Stryfe was nobody's replacement.
A/n: Yes, I know, this would never happen in the canon, and Meryl would probably die before she left Vash. I just wrote this as a What If? sort of thing-and because the comparison between Meryl and Rem were so blatantly obvious in the anime.