Is it possible to restore a deleted transaciton? Or is there a reccomended approach for importing it from the sandbox?

Not possible to restore, short of a full backup restore from NetSuite, which takes a long time and costs many thousands of dollars (and you won't have all your other changes that occurred in the meantime). No specific recommended approach afaik other than making sure you've got all your approvals and documentation on the transaction(s) for when the auditors come around. And maybe anticipate that they'll want to audit your deletion approvals going backward.