Well, first of all, you have the order of the transmission fluid path incorrect. The trans fluid exits the trans, goes to the auxiliary cooler in front of the A/C condenser, then goes to the radiator's integral cooler where it is warmed or cooled, as needed, before returning to the transmission.
The affected models are 2005 through 2010. Those are the models for which Nissan extended the warranties. We have had only a few 2009-2010 models report cooler failures on these forums and most of the failed units have been on the 2005-2007 models. We have not had any reports of failed radiators on the 2011-and-newer models. Cooler failures have only been reported on the genuine Nissan radiators (made by Calsonic) for those years listed.
That said, a cooler failure "may" occur on any radiator with an integral cooler, regardless of manufacturer, make, model or years. Those failures are pretty rare (the subject Nissan radiators not included). Transmission coolers and even engine oil coolers have been installed inside the tanks of radiators for decades and have proven to be a very reliable design.
I can't speak for your friend as I don't know him. I'm a former Nissan Master Tech and worked for Nissan for 16 years, but left in 2003. In those years, I've met some excellent, knowledgeable technicians at several Nissan dealers and I've encountered a few that I wouldn't let touch my bicycle, nevermind my car...and everything in between. I moderate these forums and NissanForums.com, as well as participate at NissanHelp.com and ClubFrontier.com when I get time. If someone on these forums had had a cooler failure on a 2011 or 2012 model, I'd love to hear from them!
As far as whether you should bypass or not, it's really up to you. If it were mine, I wouldn't worry about it. Many have bypassed and have had no issues, but I always recommend against it for those that tow heavy loads or live in areas that see extremely cold weather. Those that bypassed have found using the factory installed, auxiliary cooler to do a sufficient job of cooler and added a second, auxiliary cooler is not necessary.
Transmission oil temperature (in the trans pan) runs ideally in the 175-200 degree F. range and should not exceed 275 degrees. The converter outlet temperature should not exceed 300 degrees F. and this is the place where temperature should be monitored. Those that have monitored transmission fluid temperature that have bypassed the radiator's internal cooler and run just the factory auxiliary cooler typically report seeing temperatures in the 150-165 degree range. Transmission fluid should operate at a minimum of 150 degrees F.
The other thing about installing a second auxiliary cooler is that for approximately the same price of a quality, aftermarket trans cooler, one can purchase a new, aftermarket radiator, replace the radiator and retain the use of the radiator's internal cooler, which, being a liquid-to-liquid cooler, is far more efficient than an air-to-liquid cooler.
Hope this answers your questions! BTW, I own a 2006 and 2008 Pathfinder. I replaced the radiator on the 2006, first, and bypassed the 2008. About a year later, I got a good deal on a Koyo radiator and replaced the radiator in the 2008, as well.