I would think the swap for credit is a liability. Look at all of these folks with hundreds in unusable credits (nothing worth buying) sitting around bitching now. If VMP folds, there's going to be legal fights for that credit to be refunded i.e. debt. If VMP is stuck unable to fulfill existing orders due to a lack of cash flow, but they owe people either product or cash back, that's a problem. Credits are money paid up front i.e. loaned to VMP without fulfillment if unused.
If you "close the loop" with each customer transaction- they either buy something by choice, VMP picks something for the customer, or you don't buy anything--then you don't have these piles of credit, it's cleaner if they are forced to close. Also easier to deal with Shopify and accounting-wise, rather than tracking all these credits year over year.
I am surprised they haven't had limits around credit, such as it must be used by end of each year or if they could, they'll refund it.