Sorry, they were both wrong (kinda).
You can redirect SESSIONs using mod_rewrite but ONLY if they're not in COOKIEs. If they're attached as a query string, you can use RewriteCond to view, parse and take whatever redirect action you need based on the contents (provided you know what to look for).
That said, both previous answers were also correct - but WHY go off to another script to check SESSION variables when you should be doing that in the scripts that will use it? Sorry, that just doesn't make any sense to me.