Campaign endings and the credits mission
Ah yes, the ending movie for a campaign. A grand finale that leave the players with a sense of accomplishment and satisfaction, and finally rolls credits to let them know who brought them the masterpiece they just experienced. And currently not possible without going through some workarounds.
The main problem lies in FS2 not allowing movies to be played after a mission has ended, but only before one starts. The second problem is that this movie is fixed, it is not possible to make the movie change based on certain outcomes the way the ending for the FS2 main campaign does. Both these problems can be solved with a Credits Mission.
A credits mission is just that - A mission that serves no other purpose than rolling credits for a completed campaign, usually using training messages. The advantage of having one or more separate missions for this is that you can play a movie before it starts, and you can make the campaign link to different missions depending on the outcome of the last 'real' mission played. So you can play a movie immediately following the last real campaign mission, and you can choose which movie by linking to different missions.
The two things to remember if you choose to use a credits mission to round off a campaign is to set the mission to have neither briefing nor debriefing, and to have the end-campaign event there rather than in the last real mission.