Yes, the original letter had (for an official letter) quite some serious allegations, insinuations. If after a week, they decided not to back up their claims, I'm not sure there is anything big coming.
On the other hand, if they had some serious concerns, serious enough to fire the CEO in such a disgraceful way, I don't understand why they don't stick to their guns, and explain themselves. If you think OpenAI under Sam's leadership is going to destroy humanity, I don't understand how they (e.g. Ilya) reverted their opinions after a day or two.