I don't think so. IMG is the only player in town with TBDR, which is ideal for mobile. That'll give them a clear edge methinks.
Considering how important perf/W is nowadays even for high end designs I don't agree that the DR advantages are exclusive to the ULP SoC space. Other than that since nothing is perfect, there are both advantages and disadvantages to TBDR.
Any reason to believe that with Nvidia and now AMD, IMG will fall behind in mobile GPU performance?
Let me flip that coin for you on a hypothetical basis: if IMG would think to re-enter the standalone GPU market would you be worried that AMD and NVIDIA would fall behind in standalone GPU performance?