I think many plumbers will run water while snaking to float away the junk they are cutting and loosening up.
Putting a camera down the line might show the condition of the line, and problems. Once a pipe leaves the house, anything can happen. Tree roots, the ground settling, or even someone punching a hole in a line after the fact.
I wouldn't assume there needs to be a replacement unless I could clearly see it on video.
Sometimes you cut a few roots out and you're good to go again.
Your insurance doesn't cover?
I've heard of insurance not covering the plumbing work itself, but often it will cover the damage to the home.
If the plumber was called out on a main line backup, it sounds like it was already a problem.
Sorry it's a mess. My daughters home needed carpets after her husband notice the toilet overflowing the bowl, and then going back upstairs to shower and clean up. When he came back down, all that shower water had forced more sewage out of the toilet bowl and ruined even more carpet.
At least at that point he quit using more water.
I've run a snake a few times over the years, and you would think that someone would be paying attention to the water on the floor.
The idea is to make less of a problem, not more.