Some of our weapons now we (HQ) do not put front or rear sights on when issued to the field. They (HQ) have not had any issues with the scopes loosing zero or breaking while in the field. At least none or very few have been reported. Not enough to compel the service to spend the extra $300.00 for flip up FT and Rear sights.
My advice is to pick a reticle design you can live with and go. They are great pieces of gear.
I suggest the TA31F. I have one and love it. I originally had the TA01NSNDOC, which is a lot more money, but traded it straight up for the TA31F. The range finding with the chevron is easy. The chevron seems much more crisp than the other reticles. For my eyes at least, the circle and hoarse shoe reticles don't give a precise aimimng point. My eyes pick up the red color more quickly than the yellow (when on the move/ multiple targets). And the green is almost too bright for me. Sorry, I got to rambling. The trijicon Rep out here is awesome, and let us T&E a bunch of them.. Just my thoughts.