As per Process, it is highly recommended to customers who wish to OneWorld Upgrade to have it tested in SandBox account. This is to eliminate or reduce the risk of any adverse and/or unwanted effect of having the feature enabled.
A SandBox refresh completely overwrites the SandBox environment so that it mirrors the production environment. In that regard, if the SandBox is upgraded to OneWorld while it is not yet upgraded in the Production environment, then the feature will also be removed from the SandBox. If the Production environment is upgraded to OneWorld, then the SandBox will remain in OneWorld.
In cases where the OneWorld has been removed in SandBox due to refresh and the customer needs to have the feature turned On again, then they have to request it from Support.