If they close the tab on paypal and dont return to the store, it will NOT complete the process, and you will have to view your order details like an abandoned order or incomplete order. If you set paypal correctly, paypal will notify you of payments for orders posted there. You CAN find the order details in they mysql database, but not in the back end of the store. This is common for paypal. Thats why its crucial to make the auto return and put in the correct url for the order to show PROCESSED in your store builder. CHeck the osc manual, or scan their forum, cuz the return page will be the recipet page that is processed on your store, and not just a thank you page. If you cant find that info, then CREATE a page in OSC that thanks them for their paypal order, and have paypal return to that created page,(note this page does not have to appear in any menu system, just exist within osc generated pages) in doing so, the redirection script should pick it and return them also to the reciept page. Your created return URL link will be something like
www.yoursite.com/thankyou.php
Id have to go play with OSC to figure out what the url is that is generated for the reciept script to run, and I just dont have time right now.
Karen