To recreate vars_config.inc.php, I belive you need to go in and submit the Primary Settings of the board with the UBB Accelerator enabled. The UBB should do this whenever you submit that page. The vars_config.inc.php shouldn't just automagically disappear. If it keeps doing it, someone is probably deleting it.
Unfortunately, when you do the move instructions, it assign a new ubber id for the cookies. If you wanted to automagically accept their old cookie, you would need to write some script to read the old cookie, and set a new one. Generally, it is more efficient to just let them login again. Plus it is a good opportunity for you to possibly do a rules check or something <img src="https://www.ubbcentral.com/boards/images/graemlins/wink.gif" alt="" />
BTW, nice usage of the ubbnews.php <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" />
