My tank crashes in the past always happen when I am out of town, I have a tank sitter stay at my house now so I can worry less.
Having everything labeled well and clearly marked where sump levels and tank levels can be becomes important for someone who is watching your tank. Also having a plan and numbers to call if there is an emergency can save your tank. I have a couple reef friends who live close by that my tank sitter could call if they cant reach me on top of that they have the owner of Age of Aquariums phone number if there is an emergency. Dan at Age maintenance company has my card on file to make repairs or change out a pump if needed. Having your Apex set up with alarms is great, but unless every part of it is backed up with battery back ups you will not get the message. So at my house the battery back ups are on the Apex, a Router, and the Incoming internet. I have had a whole house back up Generator installed, but if this has a problem I still have a Honda ready to go and the 5 outlets are labeled that will give my tanks the life support they need to make it through a power outage.
I go over with the tank sitter where every water level is and even put up post it notes on the levels I want them to check and show them where they should see surface agitation when they look things over.
I also pre thaw out food and line up shot glasses with food for each system in the fridge as I have had problems with tank sitter over feeding. On top of that I do have auto feeders that drop a small amount of pellets three times a day.
I personally like Tunze top offs yet I run them to my own peristaltic pump, and I have two completely redundant top off systems in case a pump or sensor fails. I also have them on my Apex so I can turn them off if the sump level gets to high.
I have video cameras on everything so I can tune in and look, with that said I have had to let go when I am out of town as the wife would get irritated that I was too preoccupied with tank and it would add stress to our vacations. My Reef friend who watches over my tank has strict instructions to not call me even if the whole thing dies, my vacations have been better and I know with my friends in the hobby I can recover from any crash.
The hardest part for me is the fish, and I quarantine everything because I have wiped a tank out with Velvet and watching all your fish die is the toughest part of this hobby. I do what I can to minimize this possibility.
It is not if it is when so back up your favorite corals with friends and being generous gets paid back when you do have a crash.