If you really did delete it you need to reinstall Mavericks by restarting and holding the Command and R keys. Then select reintstall Mac OS. If you just removed it from the dock, see if it is still in your Application folder. If so, drag it to the dock.
You should always use an external hard drive to maintain a backup of your data, but a simple reinstall will not delete data content...it only reinstalls the operating system. Just be careful you o not o an erase and install as that will delete everything on he drive and then install Mac OS X.