Well, like Soros on the Bank of England or the attack on Terra luna, you can short SEI before the attack as well.
This is actually why "proof of stake" blockchains are fundamentally flawed. They only make sense if the value of the system is denominated in the currency of the system. It's self referential and prone to negative feedback loops. They are secure because the token is expensive, the token is expensive because it provides a secure platform. Short the token, take a loan out, compromise the security, tank the value, profit. All the mechanisms to prevent that are built into the system, like delaying the validator pool entry, but the only real backstop is a hard fork and spinning up a new copy.