I am responding to your call for an explanation of setting an alternate path.
Attached is altpath.zip, a mission to illustrate this. Included in the zip is a custom loadout for the mission (Rocknmav.ldt) which is to be placed in the \F-15\resource directory, and a wav file which is triggered called GMTBOSS.WAV which should be placed in the \janes\f15 directory.

Alternate Path:

Note: I have not tested this, but it is my belief that an AWACS object is necessary for ALT PATH stuff to work! The AWACS gives a message alerting you to the new mission. Not sure what happens if there is no AWACS, JSTARS etc..

1. Create the alternate path action.
In this mission it is by AREA EVENT, which, as has been observed is the easiest event to use!

In this mission, when the player enters the area box around WP2, The ALT PATH is triggered, by adding an Action of ALT PATH to the area event. (In this mission, a Flag is set as well).

2. Create the ACTUAL ALT PATH

Click the alt path Icon (the curving arrow). You will get a message to place the path.
I believe the alt path can ONLY be set for the PLAYER aircraft/wing so there is no need to specify this. Also, there can be ONLY 1 alt path event per mission (I think).

Click to set the alt path waypoint. It will appear on the map as an isolated point. Add additional waypoints in the usual way, by clicking the ADD WAYPOINT icon, then click the ALT PATH start point. ALT PATH waypoints are connected by dashed lines.

That's it!! When the conditions are satisfied, you will be notified of a new mission and the ALT PATH waypoint becomes your NAV POINT 0A. Remember to revert to NAV STR in case you are in TGT STR mode.

In the attached mission, there is also a FAC (who is utterly useless, but what the heck!).

email me, bobtull@planet.net for any questions.