So you just rebooted your device and Zooper Widget PRO disappeared from your home screen? Well sadly, this is not a ZW issue, but a Google problem and I cannot fix it.
Basically, some releases of the Play Store app are ignoring the “InternalOnly” directive inside the installation package. What this means is that ZW will be installed on the SD or on a protected area, and the Launcher will not be able to load the package after a reboot.
This is a known problem and is tracked as an Android bug here and here. Apparently it is fixed however on some devices, but the Play Store is still buggy. This issue affects only paid widgets. Free ones work properly (so, you may also see this behavior with other commercial app widgets).
WORKAROUND Currently there is a workaround: if your phone is rooted use Titanium backup, and save/restore the app. This will force Android to install the APK manually thus bypassing the Store issue