If I am not mistaken then the anonymity set can not decrease. Even if they stop the campaign, there will still be said 567 deposits and that number will not decrease. From that point on, every withdrawal made on the site could originate from one or multiple of the 567 deposits. Stopping the campaign would probably lead to people withdrawing their coins and the anonymity set increasing slower but it could not decrease.
According to FAQ
[1] anonymity set is the number of deposits from which your withdrawal will potentially originate.
it is a reflection of the number of deposits that may be the input of your transaction, and if the number of depositors decreases, then the Anonymity set should decrease, so the stability of the number with a small number of depositors is misleading. Generally, we have to wait for confirmation from the campaign manager.
[1]
https://whirlwind.money/My take on Whirlwind is that at least the person who uses the bitcointalk account is indeed very intelligent, the concept and the idea of the mixer are pretty unique and interesting and have great potential, however, the overall management is pretty bad, lack of support, slow Email response, being inactive on the forum -- all fall under "bad management".
TheQuin is a case in point, it wouldn't be hard to find someone on the forum who has a good knowledge of how whirlwind works.