I dont think we will have the return of $2000 pc if AMD folded. For starters, even if it went to bankrupcy, some company will buy them, provided the price is right, so AMD will go on.
What will happen, however, is that Intel will no longer need to have so many different cpus like they have now, like pentium G, celeron, i3, i5, i7 etc. These wont be needed, since all of them are basically positioned agains a competing AMD product. What I see happening is the pentium g and celeron will become the new $100-250 cpu line, I3 will be discontinued, I5 will be in the 300-450 range and I7 up from there.
So cheap pc will still be around, you just wont get the same performance per dollar as now.