Meant to disconnect from chat, accidentally deleted a DM from someone but no idea from who, is there a way to "undo" that?

I have no idea who it was, but the disconnect from chat button is RIGHT next to the "X" marks when you're looking at your DM's, which is probably bad design. Hoping there's a way to "undo" an accidental deletion?

If not, there really should be. And for the love of god, fix the freaking "maximize window" button in the corner!! How on earth has this not been fixed yet?!