Assets and CIs should never be deleted directly after retirement. Check whether the company has any existing data retention and archival policy. If there is no existing policy, check whether they need it at this point. If they are in the initial stages of ServiceNow implementation with less amount of data populated, it may not be needed soon (as it becomes important only when the volume of data becomes huge). But it is still a good idea to define the policy during the initial CMDB & asset process definition itself. For example, archiving CI data after 2 years and then deleting from the archive after 5 years or 7 years is often a standard practice.
But even while defining an archival and retention policy, it is better to define it only for CI classes which do not have an asset associated with it. That way asset data will be always retained in the system. Asset data might be required in future also for purposes like audit, compliance, sustainability reporting etc (This point is valid for some CI classes also and that is why deleting should be never done soon after retirement).
Only when the asset data itself gets huge, archival and retention needs to be considered for those. In that case, it would be better to define a longer retention time period before archival and deletion (compared to CI classes which do not have assets associated with it)
