You can use a feature called secondary-path. For this, you would use one of your other ports as the secondary path, and it would simply maintain the original state. For example, if box A is master, and box B is backup, then if the HA cable get disconnected, secondary path would maintain A as master, B as backup.
If you want to use e1/1 as your secondary path interface, then you would apply the command:
set nsrp secondary-path ethernet1/1