Same as any other brand, some fail, some don’t. It’s not the frame failing that is a problem for many, it’s the customer service once an issue has occured. Lynskey’ sounds like theirs is terrible.
They fixed my Ragley Ti when the downtube cracked at the headtube junction and told me why it had broken. Then they fixed it again as I was very unhappy with the initial repair and e-mailed Mark Lynskey direct. Shoot me, but I thought that was – in the end – pretty good customer service.
Obviously that’s just my personal experience of Lynskey via Hotlines and I have no idea of knowing whether a disproportionate number of Lynskey frames cracked compared to other manufacturers, but my advice to your mate would be to drop an e-mail direct to Mark Lynskey outlining the facts and pointing out how disappointed he is.
Also, I thought Lynskey’s warranty was lifetime:
https://www.lynskeyperformance.com/store/warranty-registration/
Is it a Lynskey-branded frame or one they made for another brand? Either way, I would suggest that he follows it up in a reasonable and polite way. Where did the frame crack?