tracking cookies for progress within Storyline

I am trying to research potential pitfalls for an adaptive delivery course I'm building in Storyline.  We have had many reported issues to our helpdesk from old Engage interactions and other PC-related issues (unsupported browsers, etc.) and have not tested Storylione enough across the board to be completely confident that there will be no usage issues.  What I would like to know is how sound the cookie-placing process is for course progress and how successful are learners able to leave a course uncompleted, then return later to finish.  The adaptive delivery course I am working on is for our annual mandatory training ed (think fire safety, etc.) which will be required by all staff (over 10,000).  This course is made up of a series of 5 courses set to "complete" for credit when all have been completed.   Our helpdesk troubleshooting script suggests that learners close their browsers and clean their cookie cache and temp folders before restarting the course when a course issue is reported.  Will this erase their progress for the course?  Is there something to be done other than rewriting the troublshooting script to clear out temp folders if someone gets hung up in the course?  This could be a major problem.

thanks so much,

Chris