When it comes to merging Leads in Salesforce, it's always best to be cautious to ensure there is no data loss.
For your reference, here is breakdown of how to Merge Leads from Salesforce Support.
Where Bizible comes in, is when it's time to select fields that will populate on the merged record. Upon the selection of the Master Record, validate that the Bizible fields are selected to carry over to the new record.
If there are multiple records with Bizible data, ensure that the Master Record has the selected fields for the Lead that was created first. Additional Bizible data will be present within the Insights section. Also, ensure that the email address of the tracked Lead is the email address that is retained as it will allow us to continue to update that Lead with any new attribution data.
From there, you should be free to Merge away and will continue to see Bizible data carried across the new record.
If there are questions, please don’t hesitate to reach out to your Bizible rep or firstname.lastname@example.org.