That leak is good news for the Amiga community.
You can look at it, figure out what the bug is, then try to patch the binary file in ASM just like you reverse engineered it, except that you won't waste time understanding ASM code without symbols.
There will be no proof that you used the source, hence it will be as legal as other ROM fixes done without the source! (we do it all the time in whdload slaves)
What you cannot release is a compiled version from modified sources! (although you can create one for test purposes)
Hey didn't Olaf write the Action Replay MKIII code? back in 1992 it just rocked man, I still have mine somewhere.