In order to be able to resurrect MBR, ypu should prepare its backup copy. First, you should determine which of your hard drives is the primary one - let's assume it is sda (as in most systems with only one hard drive). Let's go to terminal emulator and launch the following command to create a backup copy of MBR:
dd if=/dev/sda of=backup.mbr bs=512 count=1
This command will create backup.mbr file with backup copy of MBR. Copy it to a safe place and do not forget where you have put this file. In future, if some defective operating system damages MBR so that you cannot boot from your hard drive anymore, then you can just perform a revert action:
dd if=backup.mbr of=/dev/sda bs=512 count=1
If you need to resurrect the Grub loader, you can use this article.