Hi, I was grilling chicken and a piece fell out of the frying pan onto the gas stove for a mere second, and without thinking I put it back in the pan. We have separate burners and that area has been only used for the stove. I just realized that this can be an issue of treifa, but issue is we already ate it. The stove itself was used for DE(the other side), but not actual dairy within 24 hrs. Is there any case where bdeved that would be okay?

ב"ה Shalom If the area where the chicken fell, had absorbed dairy within the last 24 hours, it would have required to remove 2 centimeters of from the chicken before eating the rest. In your case, since as you say the area where the chicken fell was not used for at least 24 hours with dairy , the chicken did not become non-kosher. All the best