I would think with the cash they have on hand there likely won't be another offering. Acadia mentioned that there are 4,500 diagnosed Rett patients. They also say the following:
"Expect the annual average net realized cost of DAYBUE to be ~$375,000."
If all diagnosed took the drug you are talking about a max of $1.5 Billion in Revenue. Of course all diagnosed wont' take the drug. Lets assume eventually 1/3rd take the drug and you get revenue of $500 million.
Since there is virtually no marketing required as the patients are likely already aware of the drug, uptake on using the drug should be quick.