Do you not still get the issue of empty cart on incomplete orders.
What do you do is a person failed in the PayPal Standard when they come back to the website is the cart not empty?
We also got inhouse software that attempts to filter out cancled orders. But as far as I know there is no way to monitor sage pay / paypal or any other system when it gose to the payment provider and it times out, or they just close the browser.
There no 100% way of dealing with this, unless you ask the Nop Dev team to move cart items to the order system on confirmation from the payment provider.
It just seems a lot of work to rebuild the shopping cart if the order screws up.
In our case we only have a limmited number of products so for us it not so mutch of an issue as we sell specalist software for dyslexia screening that created by our in-house dev team.
I can see it been a problem for others. I may have a look in my spare time at a plug-in to sort this issue out but as I said for now looks like you may have to live with it, unless you go in to the code and made changes it your self.
But what you would have to do is cancle the current order, read the last order and then rebuild the cart for the given customer.
Sounds easy but in practice not sure how easy it would be till I have look at it my self.