Does anything happen after mission 13 that's scripted, or is that the absolute end of the game? Don't need to know what, just if. Or equally, any semi-long missions you can pick up anywhere that have mini-storylines associated with them and are slightly better than the typical "kill everyone here" or "capture prisoner". Again, don't need to know what, just if.

If not, are there any plans for (or existing, for that matter) Total Conversions/Mini-mods that would add such missions?