Hello, what ends up happening to Preliminary exams will likely depend on the COVID-19 situation and the current lockdown, and what the government will decide to do after 30 July.
Considering the current situation, however, it would be quite difficult to have students come to school and sit their exams like they would under normal circumstances. The good thing about Preliminary exams though, is that schools have more control over them, leading to more flexible arrangements relating to how and when students will sit and complete their exams.
As a start, schools may delay the dates for their respective exams with the hope that the situation will improve soon. If the situation remains the way it currently is, schools might be forced to find alternative ways of assessing students, which could include writing Preliminary assessment tasks that would replace the Preliminary exams, to be completed and submitted by students online. That way, students can still be assessed and their health will not be at risk. While I doubt schools will cancel Preliminary exams or replace them with estimates, this option might be considered as a last resort if the situation worsens beyond the ability of schools (i.e. gets out of control).