I think if the amp was pumping continuously at high volumes for a long time at 2 ohms, then maybe, maybe the amp can fail. The common use for the HT18 D4 is 1200w at 2 ohms. But as we all know, high impact movie scenes happen in spurts. Many here have iNukes for some years using 2 ohms and I personally have not seen anyone claim a failure.
Panasonic AE-8000, Carada BW 120", Paradigm Studio 40v3 x 2, Paradigm 690v4, Paradigm ADP 470v3 (rears), Micca M-8C x 4, Volt 6 x 2 (SR), SI DS4-18 in 12cuft X 2, Marantz 7702MKII, OPPO 103D, Emotiva XPA-3,