I have been following AMD for a while as an investment. AMD is doing much better than it was, making a little profit, making its schedules and moving forward in GPU's and APU's. Of course we know about the huge console chips in massive production. The new AMD 28nm Beema and Mullins APU's are low-end, but apparently power-competitive with Intel, with superior graphics. The recent AMD 28nm Kaveri APU is the very first HSA-enabled chip in history, not a top-end chip, but we should expect a lot of improvement to come. No Intel chip can do HSA / hUMA tight CPU / GPU compute, which may make a difference someday.
But where the OP talks about "coming back," that would be coming back to be a semiconductor chip business of decent size and profit, not coming back as in competing in top-end CPU's. Apparently the immediate goal for AMD is to move into markets which are poorly served and away from Intel dominance. That includes mid-price APU-based computers and ARM, but no classic big-core enthusiast CPU, at least for the time being.
Keller has been back at AMD for a couple of years now, but it takes 3 years or so to do a chip from scratch, and there was no time earlier, so a from-scratch stand-alone CPU may not be in the cards. However, AMD is innovating a new chip design method with a modular floorplan for the SkyBridge 20nm APU family in 2015. There would be one basic SoC layout, with space for 2 compute modules. Typically, one compute module would be an iGPU, with the other being one of: x86-64, ARM 64, low-power x86-64, and low-power ARM-64. So Keller is overseeing the development of 4 at least somewhat different compute cores for 2015, plus the K12 high-performance ARM 64 for 2016, and probably a high-performance x86-64 for 2016, with all developments feeding off each other. Apparently this has already been going on for some time.
Most of the known AMD projects are APU's, which may not get much respect from enthusiasts right now. But AMD has some innovations which Intel does not have, and with this new area of HSA / hUMA tight CPU / GPU compute, the AMD implementation patents may have the teeth to protect their market investment. However, perhaps the main reason for future AMD HSA-enabled APU's is that HSA provides a single on-chip hardware interface for the different compute modules, thus supporting the creation of a range of related products for multiple markets with minimum engineering expense.