Do refunded items go back on general sale?

If a full refund is made then the entire contents of the order are refunded and available for purchase again.

If a partial refund is made BUT for the entire order line eg customer ordered 2 x Santa's Grotto tickets and both were refunded then both slots are available to purchase again.

However, if a partial order line is refunded - eg customer ordered 2 x Santa's Grotto tickets and only one was refunded then the system doesn't automatically take this into account. Therefore you would need to make more available again by upping your original stock qty.