Well, I mean technically Sighax suffers the same risk as A9LH I think. Like the exploit associated with A9LH can't be fixed, I think, because it exploits the NFIRM, and the bootrom loads that first, and since the verified in the bootroom can't be patched, any version of ARM9Loader will always run. So technically, A9LH couldn't be patched, but it could be overwritten without FIRM patches. That being said, I believe if you still have ARM9Access, and the OTP, you could reinstall it.
Sighax could ALSO be overwritten without proper, as it simply would reside on NFIRM as well. But as long as you have ARM9Access, you should be able to install it again.
So technically, wouldn't Sighax being able to dump OTP mean that A9LH is just as unpatchable as Sighax is?
Correct me if I'm wrong though. My theory is based on the idea that to block a broken version of ARM9Loader, the bootrom would need to verify differently, but since it loads NFIRM directly, it's impossible because there's nothing to update the verification of NFIRM with, if you have access to the keystore. (Which OTP gives). Is this incorrect?