Regarding prsi, you need to fill up a form which usually is at the back of the maternity benefit form - this form must be sign by your employer and return to the prsi section which in turn will credit your prsi so you don't lose anything out.
Regarding VHI, my company has always paid in full my VHI even on unpaid maternity but not for the pension. They did not contribute for my pension when I was on unpaid maternity leave.
Regarding share option and company car, no ideas - we don't have any !!