As with any open source project, there is always the long term risk that the project in question might be abandoned some time in the future, due to lack of resources or interest.Is there any potential long term risk with Oracle reverting ZFS to closed source and OpenZFS developing independently?
My view (FWIW): OpenZFS has less chance of getting abandoned than FreeBSD, because it is used by more projects.
If you are planning for the long term, it is wise to think about / have a plan for what you would switch to if your favorite open source project dies.