Yes you can safely leave your CrockPot or Slow Cooker on high while away from home and at work as I do it all the time and have done so for many years without any problems.
If the food in the slow cooker requires water just make sure it has plenty of water in it before going to work or going to sleep and it should be just fine as long as the cord is in good condition and the slow cooker is working properly.
Slow cookers are designed to cook foods while away from the kitchen or house and many people including myself use slow cookers or crockpots overnight or while away from home to slow cook food so it will be ready to eat when we get home from work or wake up in the morning.