TR 4100 covers this really well.. a really nice reference. See page 6. a LIF migrate and vol move are non-disruptive to SMB 2 and SMB 3. lif migrate is disruptive only if SMB 1.0. An aggregate relocate (from takeover/giveback or by command) is disruptive to SMB 2.0 though but not 3.0 with CA.
Judging by the fact that NetApp created a solution to make sure SMB1 will still work, I guess NetApp left it to the Windows environment to decide if they will eliminate SMB1 or not. Security engineers may not like this. lol
In order for the LIF migrate to be nondisruptive, the SMB 2.x and 3.0 connections must establish and maintain a durable handle to the open file handle. When a LIF is migrated between nodes, those SMB 2.x and 3.0 clients with durable handle connections have their handles put into a temporary “disconnected” state. In order for the file handles to remain open, the client applications need to reconnect to the “disconnected” file handles
All this tells me is that I cannot guarantee to my managers that there will be no outage in CIFS. You are right, I am not sure how to identify that "durable handle".