I honestly don't really know the answer to your question. There's probably a rule written down somewhere about it, either none, or once, or two times, or three times at most. It might depend on the abbot.
But it ultimately depends on the person's mind.
He who is stained (with defilements) without self-control and truthfulness, is not worthy of wearing the yellow robes.
He who is purged of all stain, is well-established in morals and endowed with self-control and truthfulness, is indeed worthy of the yellow robe.
And there is no limit to how many times a person can establish themselves morally and then falter.
But unless you're an all-knowing Buddha, you have to practically draw the line somewhere. A strict person might refuse to ever allow anybody to re-ordain, while a liberal-minded person might allow them to re-ordain up to three times.
Anyway, I know you're just talking about monastic disrobing... But about disrobing in general, Mark Twain once said:
"The clothes make the man. Naked people have little or no influence on society."
That last part isn't helpful at all, but I thought it was funny.