Just to be clear, this is an edge case scenario (that might warrant a fix), but not how the majority of people use Nunchuk. When you create the key or hot wallet, best practice is to back up the key at the earliest.

This scenario you ran into is specifically about deleting the hot wallet (without having backed up the key) AND reuse the same key in a multisig.

We currently disable exporting the seed phrase more than once, for security reasons. After all, if one can view/export the seed phrase multiple times, it becomes a vulnerability, if someone gets a hold of your phone even for just 15 seconds.