I read the whole thing, but I'm not sure, is there a way for me to say do something on my rogue like if I'm feared, charmed, or sleeped, use will of the forsaken, and either if WotF is down OR I'm polymorphed, activate my PvP Trinket instead?
And if not, how about just one that will use my Insignia when WotF is down, and vise versa?
The short answer to both is "no, not really". The slightly longer answer I'll get to in a moment.
There's no way to use a cooldown conditional (i.e. there is no [isready] conditional) that would allow you to see if X trinket is up, if not do Y. There is also no [isfeared] conditional, for example. I need to edit in a few notes about that, now that you mention it.
You can, however, jury-rig the process by using the /castrandom command - i.e. /castrandom Insignia of the Horde, Will of the Forsaken will randomly select between the two. However, since WotF can be triggered preemptively (and it may not remove the effect you want it to) this macro is far from perfect - and if you keep hitting it the macro may well use both abilities, whether you want it to or not.