Is the following scenario possible (based on the wording in the TA) if we agree to this TA?
Yes or no.

We get a 3% raise and a 1% signing bonus based on a year in which 4.a.2.b was in effect, the company gets the FDA's.
We are out of section 6 negotiations.
"Warming talks" continue.
The economy goes south this fall and the company invokes 4.a.2.b. with the modifications included in the grievance settlement in the TA.
Since bases with less than 100 pilots are excepted, along with the 777; the pilots at HKG, Cologne, and LAX, and the 777, fly 90+ hour lines. The company also builds MD lines out of LAX and uses MEM based pilots to fly these extra lines, much like they have done out of ANC in the past.
Next March we don't exercise our option to extend the TA, and enter section 6 talks again.
Summer of 2012 it becomes apparent that the company is not bargaining in good faith so we seek relief from the NMB.
The NMB tells us to pound sand, that we've only been in section 6 negotiations 4 months, and to get back to the table.
November of 2012 a new administration is elected that is not as labor friendly as the current one.
A new NMB is appointed in Feb 2013.
The company continues to drag its feet and we end up going back to the NMB in the spring/summer of 2013 seeking relief.
The NMB, favoring management, doesn't help us.
So we arrive at the middle of 2013, or later, with no new contract.
That's 2 and 1/2 years since the amendable date and all we have gotten is a 3% raise, a 1% signing bonus based on a 4.a.2.b. year, loss of leverage, and a much less friendly environment for negotiations (vis-a-vis, a non-labor friendly administration and NMB).
The company has it's FDA's and is able to pad the corporate bottom line, via 4.a.2.b., on the backs of the pilots - again.
Is this possible?
Yes or no.

As an aside, if the NPRM is such a show stopper, how did the Pinnacle pilots reach a complete agreement a few weeks ago, with language that allows the reopening of affected sections after the NPRM is released?