The tricky part about % chance to win the playoff is that all possible matchups have to be taken into account.
Yep. So I'll make up numbers here, since I've already done that somewhat...
Clemson we'll say is 70% vs Oklahoma.
Oklahoma we'll say is 58% vs Notre Dame.
We already have Bama:
Alabama(Champion) = (.728 * (.64*.714 + .78*.286) ) * 100 = 49.5%
Clemson(Champion) = (.714 * (.36*.728 + .70*.272) ) * 100 = 32.3%
Oklahoma(Champion) = (.272 * (.30*.714 + .58*.286) ) * 100 = 10.3%
Notre Dame (Champion) = (.286 * (.22*.728 + .42*.272) ) * 100 = 7.8%
That all adds up to 99.9, so obviously once you account for rounding, we're at 100%.
Now, I simply made up the potential win likelihood for the CFP matchups because I couldn't easily find them.
But if you were to know the potential likelihood for those games, you could just plug in the correct numbers and fix it.