It is not good practice to overstay your visa in any country. It will be stamped on your passport and recorded online these days. You could be fine or you could come back and pick the wrong immigration official coming back and have issues it’s up to you what you choose to do
from experience it is all done via agents in Phnom Penh or certainly was when I did last. There used to be a fast track but it was still a couple of days to get done I did read somewhere recently they had stopped the fast track but can not remember the source
I’m the same had prepared for Vientiane visa run but this was easier and better as long as you are a director they didn’t seem to be insisting on MD title when I went a couple weeks ago
You can obtain a work permit on a visa O marriage or supporting child also and it does or did mention assistance in getting a work permit in their blurb so it may be possible on an elite visa best to discuss with them directly to check