Remember, even in the Age of Legends, ter'angreals weren't something that people could just MAKE. As far as I can recall, none of the Forsaken have any particular skill with them. So it's probably a matter of how extensive the DO's knowledge is, how much of it can be communicated to Moridin, and how able they are to replicate it....before the Last Battle.

I don't think we'll see any serious consequences from the Medallion escaping. I'm sure, however, that Mellar will not give them up lightly and I would not be surprised if we see them again.