There are different types of chips. Most are cracks, or pockets of air or a combination of both. The 8mm 'crack' described by the OP is part of the impact and an experienced repairer with the right equipment should be able to address the problem.
1) An inexperienced repairer who will blag and bullsh*t his way through convincing you that the repair he has carried out has been done so correctly. If it still looks the same, it has not been done correctly and you should not accept or pay (or authorise them to bill your insco).
2) A 'qualified' repairer with a piece of kit that is not really that good. By this, I mean if he's getting you to sign a disclaimer enabling him to walk away/bill you/bill your insco should the attempt to repair fail, you should really think twice about signing that disclaimer. Stonechips 'cracking out' whilst being repair is not as common, or expected as some repairers will have you believe.
3) all of the above.