Do I need to renew the Institutional Recovery Key certificate with FileVault
I advise you to test this by setting a test Mac and then starting it with a date set to April the 1st of 2019 (just after your certificate expiration date).
Of course, for this test to work you will need to deactivate any automatic time synchronization:

System Preferences... &gt; Date &amp; Time


turn off:

Set Date &amp; Time automatically