If I erase my iPhone remotely, what happens to my iCloud backup?
The backups do not get erased when you send an erase request to a phone.  You are actually preserving the back ups in the sense that if your phone doesn't have a passcode lock or the passcode becomes compromised, whoever has your phone now could start deleting things and if the phone starts  A new back up then your current backup would have less of your data on it. 

The interface for deleting back up data of an iOS device is in the manage storage portion of iCloud. If you think someone has access to your iCloud account, change your password to prevent them from deleting the data.

So, unless other things happen, your back up data will be sitting in iCloud waiting for you to load it on your device if you recover it or on another device of your choosing.