I would take Ibis up on the crash replacement while you're within their warranty period (whatever that may be). Carbon repair is 100% legit (friend has been full sending his carbon patched Capra for a year+) but will tank the resale value of your bike.
If Ibis doesn't need that frame back, you could get it patched, ride it until you decide to sell the bike, and swap the brand new frame components on for higher resale.
If Ibis wants their frame back, then it gets a bit more complicated should you repair your bike. They may not be stoked about any further warranty issues if you've been knowingly riding on a compromised frame. This isn't just about this one crash, what about damage down the road?
$600 isn't a small amount of money, so I understand your hesitation, but it's probably the most responsible thing to do. Plus, if you don't need to send back your frame, then your long term options increase.