Plumbing rectification by relining pipes

Internal relining is a well proven technique, that is widely used by Water Authorities. It is rarely cost effective against the replacement pipework using more modern materials such as PVC, unless significant sections of the existing infrastructure is damaged and excavation works to replace it is difficult (e.g. rock, trees), and remediation (e.g. to landscaping) is extensive.

I have no axe to grind either way, but in one of my past lives (at GM level in large State-Owned Water Authority) I've seen both PVC sewer pipes and internally re-lined VC pipes that have been extensively damaged by larger tree roots.

Conversely, where the conditions are “normal” I've seen both materials last for 25+ years.

Whilst the epoxy lining used in the relining process is continuous (no joins) and that does indeed prevent the ingress of fine tree roots, if the trees that you're referring to are within a few metres of the sewer pipe, then their larger roots will lift and/or depress sections of the the pipe, and blockages due to sewage residues inside (as opposed to fine roots from outside) will still occur and mechanical “cutters” can't be used to clear those.

Whatever pipe replacement method your Plan prefers, I'd first speak with a couple of experienced Contractors about the options to relocate a new sewer away from the trees altogether, as even if that work is completed in sections over time in order to stage the costs, it's the only long-term solution.

Good luck with Local Government; I never had much success.