Regardless of his choice, the finance is linked to the car, and there must be a clause somewhere in the contract re rejection of car under Mutual consent. As yes he is terminating the cars agreement, however he is replacing it with liek for liek finance, You should end up having some of the interest rebated.
Remember on a repayment loan (where you pay capital and interest) the interest is top loaded, therefore if you settle early you are entitiled to an interest rebate. This is beacuse to work your payments out for the full 4 yrs they have to assume it runs the full 4 yrs, so they work out the intwerest for the full period then divide it by 48 ( an example) but if you stop paying after 6 months etc, you should then be rebated the excess interest paid.
To be honest its very hard to know whether you are getting a good deal or not without seeing all the figures and also being privey to all the discussions you have had, the deal is done now , so can't see what else you can do now. just keep your fingers corssed it does'nt happen again i suppose.