If it's a through fare then the airline will take care of the rebooking if he misconnex, but if it's two tickets then indeed he will not be able to make any changes without paying the applicable fees.
Indeed, a through fare with LA
/KL seems strange, but is actually not impossible... Once I booked a ticket for a customer with LH
and the routing was with LH
and then with Sky (!!) to SCL
. Til that point I didn't even knew that LH
and Sky cooperated for flying beyond LH
He can see if it's a through fare by looking in the fare calculation of the ticket. If the receipt shows something like "SCL LA
X/SAO KL AMS
[an amount]" it would be a through fare while something like "SCL LA
SAO [amount] KL AMS
[amount]" would be two different fares priced on one ticket.