For those of you having trouble with 13, you want to spend a minute or two observing the fighters' paths before you head in. You will notice that heading straight in is
not the optimal path to the target. Instead, you want to fly around the "sphere" of fighters and approach it from the top or bottom. This is described in the walkthrough.
In any case, the updated version of this mission will adapt to the difficulty setting. It should now become a walkover on very easy, well, unless you really suck.

When you say you've fixed the issues, will we have to redownload it?
It's a patch file containing only the modified data. You don't need to download the whole thing again, although I will update the main download as well for people who haven't downloaded the campaign yet.
I'm interested in Dasmar's plans. What was that Ancient Device for? What does he mean with return?
I'll post a detailed explanation in a day or two. I had written a bit of an essay in response to this last night, but didn't have time to finish it.

I plan on installing this new campaign tomorrow but I just want to make sure that all that's required is to download all of the links provided on the dl page?
Yeah, that's it. They don't replace any FS2 files. You might want to wait a bit though, as I'm planning to release the patch tonight, so you can just get the updated version.