Is there a reasonably up to date offline tool for writing missions?
To my understanding, there isn't. You could possibly use it as a starting off point and then adjust it more once imported to the game. Also, since it is technically just a text file, you could type things in by hand though that would likely be very tedious.
If I can find the time, I'm planning to create one this summer. So go ahead and chime in with any feature requests now if you like.
I'd say the main thing would be simply to match as many functions as the current creator as possible and make sure the export functions create a valid file for MA use.
When the MA first came out Leandro had a great little tool for writing up most mission offline. I'm wondering if there is anything that is more up to date than that one.
My first short story (detective fiction) came out in Jan-2012. Other stories and books to follow, I hope. Because of "real writing". COH was a big part of that happening.