Partial documentation combined with complex code will be great for your bank account.
Code fast, and badly, always under promise and over deliver. Before the shit hits the fan, move to another place.
Next person after you will take the blame. You may be hired again at premium as you can deliver. Blame the replacement Dev for breaking the code and causing a lot of damage.
Fix the little that is possible, at premium rate and move on.
I managed to donate a few patches over the years. But the whole ceremony with a PR around a fix is just too much. It takes more time than I have free.
I have a minor error fix sitting on my computer for over month now. No time to get it merged.
Most of it revolves around how bad the housing situation is.