You can leave it as is. Whatever watt target for braiins assumes its spread over 3 boards and the ~75w overhead for control board. So if it was 975w, it would be roughly 300w to each functioning board and that needed for control (675/975). With one hashboard down vs the controlboard, it'll slightly raise your watts/Th.

A physical consideration is to ensure the remaining good boards are not in the hot board lane, allowing you to eek out a bit more hash in the other lanes with higher temp threshold. Remove bad board or unplug its power.