you might want to take a look at deploying the ISC Governance Connector, and using its Reassignment settings:
when the governance connector account (and thus the identity) is disabled, it can perform this action.
Ive also done very similar (and then some!) in a presentation I did for Developer Days 2025
if you need this in a workflow, high level:
trigger: identity attribute changed (lifecyclestate >> inactive)
call list-identity-certifications | SailPoint Developer Community
with the query param for the reviewer-identity, and possible filter for completed eq false and phase eq active
check if that result is null
check if the identity has a manager
then loop over those certifications, and reassign them
you run a risk here however on if that identity has more than 250 active Certifications (note: not certification campaigns, just certifications)
but that should reassign up to 250 active certifications to the manager.