I'm not an iDEN user, nor really a Nextel fan, but the one thing that bothers me the most about killing iDEN is the loss of unit-to-unit walkie-talkie use without a tower needed to support it (MOTO Talk, which Nextel calls Direct Talk). When all else fails, power is out, towers are down, etc, emergency responders can still stay in touch with nearby team members with current iDEN units. That goes away with PTT CDMA (which requires connection via tower AND 3G service).
Yeah, iDEN is expensive - mostly because it is unique - but that uniqueness is what makes it the first-responder's dream.