it decomposes in the pipe. the liquid goes in the ground. the pipe is solid compost. 126' at 8" is a lot of volume.
Even with that section missing, a certain amount will make its way through. At first it will be just liquid eroding the soil to find a path. Then it will be everything. High flow periods will carry solids just like a fully functional system, but during low flow solids will not carry. This is what happens in your home system as it ages - More severe with cast iron that is rough and builds rust, but also in PVC that builds up with dried solids that stick.
To start a drift, we can expect an increase in sewer line and main issues with the explosion of low flow and water conservation. Our traditional systems are not designed for high dry matter low flow. I am not an engineer, but having dealt with our own septic system and with
four six styles of manure handling, we would benefit from small holding tanks with chopper pumps to send our sewage to the main through smaller pipes. The days of four to six inch gravity feed is nearing an end.