Kakashis kamui is even stronger than when he was able to kamui the hachibi. This is what will be the last step in shukakus plan. Kakashi will kamui the juubi, and obito wont be able to kamui it back due to his ms not being that strong, without narutos chakra of course.
Even if obito tries to go intangeble the juubi would rip him apart in the other dimension.
This will be what defeats obito and the juubi.
Even if not, the kamui will play a role. There wouldnt be 2 pages on kakashi saying how muh stronger his kamui is even since he kamuied the hachibi.

Obito wont last long if he cant go intageble. He either dies by juubi in other dimension or dies by shinobis hands.