Its quite simple...
You need two triggers, one of which you already have and then you need to know where all units/doodads are going to be at the end of the cinnematic.
In your second trigger, add the event - Player skips cinematic.
For actions simply set a global boolean (SkippedCinematic) to true and move all objects to where they should be at the end of the cinematic.
Then add ifs frequently in your cinematic trigger saying that if SkippedCinematic is = true then skip remaining actions...
-Hope this helps...