Q: CAN YOU ONLY RESTORE THE BACK UP ON YOUR LAPTOP ONCE OR AS MANY TIMES AS YOU WANT ?

Once you restore, it will create another full backup if that is what you mean by it disappears.

Time Machine is designed to backup your Mac as-is. So, once you restore, it will create a new full backup to reflect the current state of your Mac.

There is a lot of good information about Time Machine here: http://pondini.org/OSX/Home.html