gzt: That sounds very weird. It's an accident. The lease agreement that does not require or provide insurance? Hard to believe. There must be more to it surely.
Leases have a requirement that you use OEM parts for repairs, that's not a Tesla specific thing, it's just the way leases work, at least in the US. You don't have to get those repairs done at an official dealer though.
So if you return your leased car at the end of the lease and it's got non-oem parts you will be liable for the costs to replace those parts with OEM ones.