" Is this one that a repair would be acceptable and will it hold up over time?"

I'm in the stone repair business. The answer to that question is another question, "Who screwed it up?"

When you've had your drunken buddies over and you chip the countertop, it's a get-this-fixed-before-my-wife-notices-and-kills-me repair. If the repair is not your fault, as is apparently the case here, the standards for an acceptable repair can be higher.

Here is where the fabricator's customer selection skills come into play. (We flooded the same kitchen 3 times this week and the people were still happy, so I'm kind of an expert on this.) You need to gauge the fussiness and sophistication level of your customer beforehand. You can be a jerk customer and expect new countertops or you can be reasonable and accept an inconspicuous repair.

Fortunately, it looks like there is some movement in your top which makes repairs more inconspicuous. It looks kinda deep so a more involved insert repair may be called for. A proper repair is permanent. A fair standard for any repair is if a buyer's home inspector wouldn't find it, it's acceptable. Remember, you can never "unsee" something, so it will never disappear for you.

Good luck.