What is on the gateways is a "compiled" version of the policy.
It may not contain all the information you need to restore the policy to the manager.
Also, if your management is R80.x, most likely the data will be in a format that will need to be converted.
You're definitely going to need Check Point Professional Services for this.
Bottom line: you should be making regular backups of your management.
You can see a discussion of the various methods here:
VMware backup vs migrate export vs Gaia snapshot