HDD FAILURE

I have an inspiron 15 laptop.Recently one day the system hanged and after about 20 minutes, I forced-shutdown it by pressing power button.After that it showed checking media failed, unabe to find boot device and it continued twice or thrice.I contacted the dell support,they told me that its a hard drive issue and needs to be replaced and it will cost R 7000(as my laptop is not under warranty).I haven't made recovery of my operating system yet but willing to pay the price for new HDD but how I will have original version of WIndows 8 again in my laptop?This is what I need to ask?I contacted twice or thrice but all tech support persons say different things to me regarding operating system.Right now the laptop is working properly but the feeling that it might crash anytime is very disturbing as I am a student and works  a lot on the laptop. Please suggest me what should I do?