If it really was a tiny number of users, they would publically make a really good offer - for example: "Unfortunately, you will need to retune your models on top of GPT-4. OpenAI will do this for you for free, and refund all money you paid tuning your original model, and offer the new model for the same price as the original model."

The extra trust gained by seeing another customer treated that way easily pays for a few credits for a small number of users.