At least one of the computers (Colley) would still have Oklahoma #1 if they had lost to BAYLOR. Try it for yourself.
http://www.colleyrankings.com/playgod.html Certainly no drop here losing to either Texas Tech or Kansas State/Missouri.
In Colley, Oklahoma is .965 and #2 Ohio State is .891. The difference is .074, and .074 below Ohio State is just above #5 Tennessee. It is reasonable to assume that the larger the gap over the #2 team, the less likely Oklahoma is to drop with a loss. Testing the other computer polls with this example should be a reasonable test of whether Oklahoma will drop with a loss. I'll set the cutoff at #7 to allow for variances in computer's procedures.
Anderson-Hester has #1 Oklahoma at .821, #2 Ohio State at .770. That .051 gap is the same size gap as between #2 Ohio State and #13 Michigan. No drop.
Massey has #1 Oklahoma at 4.752, #2 Ohio State at 4.322, 0.340 differential. That far below Ohio State is between #14 Michigan and #15 Purdue. No drop.
Wolfe has #1 Oklahoma at 8.569 and #2 Ohio State 7.529. At 1.04 below Ohio State is #18 Mississippi. Oklahoma stays #1 with a loss.
Sagarin has #1 Oklahoma at 100.21 and #2 LSU at 93.52, a 6.69 difference. At the same distance below LSU (86.83) is just above #10 Florida. No drop here.
Billingsley has #1 Oklahoma at 334, #2 Ohio State at 308. That difference (26) below Ohio State is less than a point over #4 LSU. Oklahoma should lose a spot or two here if they lose, but Billingsley is Oklahoma based and Oklahoma-biased, so one spot at the most.
I can't test the NY Times because I'm not a subscriber. Since the lowest computer ranking is thrown out, we'll just throw this one out.
With a loss, Oklahoma is still #1 in 5 polls, no worse than #3 in a sixth, unknown and dropped in a seventh. Computer average drops from 1.00 to 1.33 at worst. SOS is 10th currently and can't help but rise playing against a 7-4 Texas Tech and either a 9-3 Kansas State or a 7-3 Missouri.
Hypothetical BCS after Oklahoma's loss in the Big XII title game to Kansas State, with all other game involving these three teams won:
Oklahoma: 1 (loss) + 0.32 (SOS) + 1.33 (computers) + ??? (polls) - 0.6 QW (Texas, assuming they beat Texas A&M) = 2.05 + poll
Ohio State: 1 (loss) + 0.36 (SOS) + 1.67 (computers, #1 from Billingsley and NY Times) + ??? (polls) = 3.03 + poll
Southern California: 1 (loss) + 1.28 (SOS) + 3.16 (computers, gaining one spot in either Billingsley or NY Times) + 1.0 (poll) - 0.2 QW (Washington State, moving up to BCS #9 with Michigan's loss) = 6.24
[NOTE: Ohio State beating Michigan prevents Michigan from being in the BCS top 10, so no quality win.]
As long as Oklahoma's poll average doesn't drop to 4.5 or worse, they still go to the Sugar Bowl with one loss.