SCOTUS will find a way to preserve the SEC as it is. It has been a very long time since SCOTUS applied the nondelegation doctrine in a way that actually reduced the power of the Federal government.

But most importantly, SCOTUS is always careful to confine their decision to the case at hand. SCOTUS's decision in the Jarkesy case would at most affect a narrow aspect of the SEC's power. And they would give Congress plenty of time to make whatever minor change needs to be made. And that's the best-case scenario for the defendant.

In other words, none of the SCOTUS judges are so dumb as to undermine the power of the organization that gave them a cushy job for life.