He will need to censor also all transactions that depend on transactions sending his funds away, and that will soon be a lot of transactions.
Not at all. For transaction sequence A->B->C and A is censored, B and C become invalid if they depend on A.
They are valid on the main fork.
Even in the case of a very swift attack, as it was mentioned, max reorg depth in NXT is 720 blocks, that's about 12 hours, there will be many transactions that will need to be censored because they depend on transactions transferring funds from the attacker's addresses. And, if you ask me, I can't imagine how it's possible to collect priv keys for stake enough for such attack in such short time frame.