I don't understand why her tweeting she's sick should have any effect on the Tony OR mean that she's likely to drop out.
She as a bronchitis that's lingering because she has asthma. She missed 4 performances last weekend, but she did the full 8 shows this week despite of not being 100% recovered yet. I saw the show today and aside from a few coughs during the beginning of the show, she would have not been able to tell that she was sick at all. Her energy level was as high as ever, she didn't miss a beat and she didn't miss a single one of her high notes either. I don't know how she does it, but she does. If you need any indication that she will NOT follow in Miss Kahn's footsteps, that would be it.
Also, Judy Kaye was just fine for several months after Madeline Kahn left.