The WSA also binds both ways, remember- GloFo are required to provide a certain number of wafers on a suitable process, just as their customer is required to buy them.
That's not the kind of agreement AMD has with Globalfoundries, as you can verify to what happened with them in 2012: By that time they had Krishna and Wichita designs ready, and Globalfoundries didn't have their 28nm process ready. What happened with Globalfoundries? Nothing. AMD had to scrap the project and Globalfoundries didn't have to pay anything due to breaches.
Today GLF's 28nm process is still inferior to TSMC's 28nm process, and what's the result for AMD? Nothing, they still have to backport everything to GLF and stick with whatever GLF can provide for them. AMD's WSA binds the buyer to the foundry, but not the foundry to the buyer. The foundry can field whichever pie-in-the-sky process and AMD has to bite it.
I doubt that IBM would accept something even remotely along these lines, and this is what should have stalled the talks. IBM has no need to be tied to a 3rd rate foundry partner, especially when they have Intel on the other side of the table offering access to their process node, probably without strings attached.
If IBM gets their predictions right on POWER sales, then a WSA shouldn't be a big issue- they get guaranteed wafers on the exact same process they would have been using if they hadn't spun off the fab.
When you have a marketing falling 20% YoY, that is certainly an issue. In fact, one of the causes of IBM quitting this business is because sales are crashing. What's POWER sales in 5 years? Will we have another 20% drops in the next years or will the drain stop?
It's not like IBM's fab is going to suddenly regress to 28nm bulk just because they changed owner.

And no other fab is offering a process suitable to IBM's needs- it's not like they could port POWER8 to TSMC's bulk 20nm SoC process.
TSMC is offering a suitable process. SUN T5 is manufactured with TSMC 28nm bulk and performs very well. Die size is withing acceptable limits (20% smaller than 16 core piledriver), clocks reasonably high (3.6GHz for the 16 core version) and it seems the customer is happy.
Intel is also open for business.
So I don't think Globalfoundries is the only game in town. In fact, it's the worst game in town.
The reason the WSA went so horrendously wrong for AMD is because they totally miscalculated demand for their x86 products.
Oh, so there's nothing wrong with one-sided take-or-pay charges, with the foundry delaying nodes and not being subject to sanctions of any kind and mandatory backportings?
PM me please, I have contract that might suit us both.