It is virtually always possible to write new code (even having to learn how to do it) than to try to reverse engineer other existing object code
I once was tasked with recreating several devices (the factory burned and no outside backup existed - they have learned and now everyting exist in two physical locations).

I did disassemble the code and found it marginally useful as far as detecting the intent of some 'strange' hardware issues; however I did end up writing the code from scratch.

At a later date I got a similar task, this time; however, the code was written in C and quoting the old song "just one look was all it took" to see that any attempt to decipher even the basic concept of the code would be futile.

In summay: The only use I hve found for disassembly has been related to hardware, not software.

Erik