No, stock quantity should be updated on order regardless the payment status because if the stock is left as is and an other user makes a second order he will have no product to get if there is only 1 product in stock. Then you will have 2 users having purchased the same product! When you make an order the products are reserved for you. If the order is cancelled/deleted the reserved products are released and become available again for other users (this requires stock to be enabled in Open Shop). Open Shop v1.x and v2.x works the same way in this.
I totally disagree. You can create a mess if you don't reserve the purchased products after an order. Consider this: You have 5 items of product A. Customer X buys all of them, the order is saved and selects as payment bank deposit. This is an offline payment method, the administrator will be notified about the deposit even 2 days later. After some hours customer Z orders 1 product A he makes an online payment and gets the product. Now the next day, or after a few hours, customer X makes the payment and waits you to send them 5 A products but you have only 4 in stock! He has placed a legal order, paid for the products and you have no product to give him. Is this right? I strongly believe it is not. You can't convince me for the opposite. Except if you want to play boxing with your customers... This is a simple case, I can make you more complex examples.Open Shop has cron jobs for various tasks but not for the task you want. But you can use Elxis cron jobs for that task.Put your custom PHP code in a .php file (any name) and place it in folder repository/cronjobs/ Enable cron jobs in Elxis configuration and you will have automatic deletion of unpaid orders. Elxis will execute any php file will find in folder "cronjobs" periodically. I believe most administrators want to delete orders by themselves and not use an automatic deletion mechanism because some orders may be delayed on purpose (eg waiting for a customer to reply, waiting for products to arrive, problems with the payment gateway, etc).
You can have problems with just paypal too. This problem is more likely to happen on a shop installation with big traffic. If the selected payment is paypal and payment fails or the customer clicks the cancel button I believe you should delete the payment after a while, you don't have to wait 7 days.