What will happen to my games data

[quote user="R0GuE DeaD GuY"]the harddrive doesnt come off[/quote]All 360 HDDs are removable. There's a bit of a trick to the one on the original console (push down on the button then remove by digging your finger into the button towards the drive casing,
not towards the console), but the one in the 360 S has a pull tab that pulls the catch which holds the HDD in place so that the HDD can be removed.

You can use a USB stick for backup (this is what I used)

Hey Smitty

Thank you for taking the time to post this on the Xbox Forums. We understand that you are inquiring about your save data.

As per the
Xbox One cloud game saves FAQ, you can choose to delete save data in two way:

• Delete from console removes the local copy of this save. You can get it from the cloud the next time you play.
  
• Delete everywhere removes your saved data from this console, the cloud, and all other consoles you play on.
  

Keep in mind that this will not delete achievements. Once you gain one of these, it is attached to your console permanently.

I hope this was able to clarify further on this matter.

[quote user="IceStorm III"]

All 360 HDDs are removable.

[/quote]

True unless it is the 4G version, that one is not.

@OP if you are referring to the 4G version then you will only need to back up your game save data, everything else including your profile (provided you know the correct e-mail and password) can be redownloaded from the XBL servers.

Also everything you downloaded you can just redownload again so you just need to backup saved-games and your profile. All demos other stuff available on the marketplace you can just redownload.