While there’s nothing technically stopping them from being able to work remotely, in practice there are local regulations in place which means traders can only operate from the business location itself, using phone lines with recorded features etc. so they are unable to do insider trading. When offices had to be evacuated for other natural disasters, different offices in other parts of the globe would step up and manage the state of play until it was safe to return. TL;DR, yes, they need to come in.