This happens more than people realize (browser crashing, people distracted, ADD etc..) - so yes, there definitely needs to be a way for a member to be able to pick up where they left off, either by following a link in an email sent by the system if transaction is not completed (within say 1 hr), which says something like:

Dear {username},
Thank you for your interest in {sitename}, we noticed that you tried to subscribe to our {package-name} and were directed to our payment gateway. If for some reason, your session timed out, your browser crashed or you had to rush off somewhere, please go ahead and complete your subscription transaction by logging into your account and clicking on the "Complete my subscription process" link which will take you to our secure payment processor where you will be able to finalize your transaction and enjoy all the benefits of paid membership at {sitename}.

See you on the inside,
The {sitename} Team

OR

They need to be able to simply log into their account (which seems to be impossible right now) and click on the link to complete the transaction. This could potentially get a lot of members upset if they are eager to sign up and pay, but for some reason could not complete the transaction and are now left out in the cold without being able to access their profile etc. Taking it a step further, the member would probably try to sign up with a new account which will only frustrate them more, since the system will no-doubt prevent them from using the same email address to sign up, plus the username they wanted will now be taken etc. etc :roll:

I see at your other post Leki, that admin is working on a fix, hope it will be available soon.