To be safe, make a back-up up copy of your entire "public" folder first. The usual way is to use FTP to copy the whole folder from the web-server to a folder on your own computer. You can even make a further back-up on a CD if you wish.
If you use extras like databases or blogs, you will also need to consider how to back up those too.
I would expect the other files to remain in place when you create a new home page. Only pages with the same name would get over-written. That said, I don't use ESW, so don't know if it clears out the whole folder first.
If you do find that files have vanished, then you can copy the ones you want back from your computer in the reverse of the back-up process.
You can congratulate yourself on asking this question before you discovered any pages had gone missing. We usually only think about backing-up when it is too late.
Nigel.
