Viking insurance will reimburse for cash for covered reasons such as getting sick or a death, ….
You just need to look at their list. Vouchers come in to play when it’s not a covered reason.
The problem is they do not insure vouchers so if you used there vouchers on a subsequent cruise and used Tripmate you are at risk. However if you used a different insurance that covered the vouchers you would be ok on that subsequent cruise.
I still prefer cash because you might want that subsequent cruise to be on a different line for whatever reason which turned out to be the case for us.