Re: I admire their spunk!
Code rot is an obsolescence variant of technical-debt which will bite you later, often as security issues (e.g. in OO probably) or as code which is hard to maintain.
Most code should be written as manageable sized modules for ease of functional testing, and for isolation to allow internal changes which won't break other code as much; it sounds like this is what the LO wisely team is wisely doing with the crufty old OO code, but the obviously Zombie OO project has shufflingly failed to do.