Zeus has recently officially implemented a personal ICS permalink feature, similar to tonnerre.link (accessible under Generate an ICS > Generate my link).
Since their implementation is provided directly from their service, I encourage you to try out or migrate to their system.
However, their implementation is not yet on feature parity with tonnerre.link, as it does not show the class type (TD, Lecture, Exam...) and class groups in the event description, which I think is an important feature.
In the event that their implementation has the same (or more) features as tonnerre.link and is stable, tonnerre.link will likely be discontinued as it will not have any reason to exist anymore.
Any discontinuation will be announced by email at least a few weeks in advance.
Thank you for your understanding.