As soon as they turn it on it will be erased.
If you erased your device, and it had iOS 15, iPadOS 15, or later installed, you can still use Find My to locate the device or play a sound on it. If you had an earlier version of iOS installed, you won't be able to locate the device or play a sound after you erase it.
If you have AppleCare+ with Theft and Loss, if you erased your device you won't be able to file a claim.
Did you contact your local authorities and your cellular carrier and report your device as lost or stolen?
Please see this: If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support