Re-activation of campus-wide licenses is under the control of the university, according to whatever procedures they have in place.
In some universities the process is completely automatic and requires only that you log in with appropriate university credentials and fill out an electronic form of request.
In other universities, there is the additional step that the university checks that you are enrolled in a course that requires MATLAB. That might or not be fully automated, so there might potentially be a time after which the responsible person does not want to bother with it.
In some universities, the re-activation is automatic if you request it by a particular deadline, with them figuring that they have already verified that you are a valid student. So if you do not reply by that deadline, they might take longer to process the request.
And in some universities, the authentication is done by Mathworks based upon you having a university email address: in such a cases, all it would mean if you do not reactivate at this time is that there would be a period during which you could not use MATLAB, which would not matter to you -- but it would matter to people who are actively trying to use MATLAB and would find that their licenses stopped working suddenly because they did not reactivate in time.
We do not know the arrangements at your particular location, so we cannot be more definite.