You either need to do some programming to stop a user from deleting an Android app, or a better alternative is to install an app such as one of these:
https://play.google.com/store/apps/details?id=com.sp.protector.free
https://play.google.com/store/apps/details?id=com.fotoable.applock
https://play.google.com/store/apps/details?id=com.domobile.applock
These apps are suggestions only. The management of your phones is up to your IT administrator.