Belly in sewer line - Worst case scenario?

[meganite]

I'm buying a bank-owned investment property and was provided a copy of a sewer line inspection a previous buyer performed. The report did not include much detail, or any photos or video. Because the inspection was not issued to me the inspector won't consult on it at all. The inspection contingency has passed, so getting a new report is not possible.

This is what is notated on the inspection report

I do have a "go-to" plumber who advised I wait on repairing it until I have to and hope it doesn't become an issue or something the Buyer objects to. Even then he only suggested repairing the exterior line and gave me a very affordable bid, but seemed apprehensive to commit to addressing the belly under the slab. Any idea as to why? For a quick fix, would correcting the exterior pipe and installing a backflow valve be a viable solution?

If some of you plumbing gurus can help me understand how pressing an issue this actually could be, I'd appreciate it. My budget is pretty tight on this one, so I really want to go the "do nothing" route, but I also wouldn't ever want to stick an expensive guaranteed repair for my Buyer. I have a very short window of time before closing and need will have to back out of this deal if it's going to be a repair in the thousands.

 

[Sylvan]

Sell "as is"

Many of my accounts have bellies in their sewer or storm system .

Depending on the severity of the belly such as cast or clay pipe usually these lines need to be snaked or water Jetted on a yearly basis

Figure $325 per year