Just sharing my thoughts...
I am not familiar with AWS cloud HA stuff, but I guess CIFS/SMB behavior should be same whether on premise or Cloud.
During NAS Fail-over, LIF (Holding the IP) will be moved to surviving Node Physical Port, it may drop 1 or 2 pings but the copy will go through. However, if the LIF (Holding the IP) cannot be failed-over, then CIFS will error-out and will ask user to cancel or retry. If you say retry, it will start from the scratch.
1. If they say "Yes", does the copy restart where it got interrupted (checkpoint/restart function), or does it start over from the beginning once node2 takes over?
Ans: Start over from begining.
2. They actually said "No" to the restart question when they tested this. Would they expect:
a. The file to be "wiped" from the target client (no data copied)?
b. The file to be partially copied over, but not completely.
c. The Windows Explorer on the target client shows the file completely copied over, but is unreadable?
Ans: a. The file to be "wiped" from the target client (no data copied) - This is purely CIFS/SMB nature, it will either commit everything or nothing (unlike NFS).