Hi Tobias-

once, 'fault'/ 'at-fault'/ 'partial-at-fault' issues have been determined (on a case-by-case basis & taking into account state insurance laws), insurance companies maximum monetary obligations are outlined within the $ limits of coverages (irrespective of "book value" coverage or "replacement value" coverage in this case)

in the event that damages exceed (the kid's) insurance policy limits, the at-fault party(ies) are then liable for the deficiency ie insurance companies are not contracted with a "sky's the limit" financial obligation

it goes unsaid that for any specific scenario/ case, both parties insurance policies would need to be reviewed to ascertain merely the contractual obligations to the insuree (fault/ no fault/ and paritial at fault matters notwithstanding)

in regards to, 'no-fault accidents' or 'no-fault comprehensive claims' being tallied against a policy holder' ($ paid out or not)- the insurance policy itself will state how these will be handled (and it would probably vary by insurance company)

On another vein- we should all know our insurance policies we purchase and spend tons of $$$ on- - to the extent that blackmercedes does!

hope this helps!
-fad