Yes, I definitely think of this possibility. I have a HOB overflow box so I only have 1 standpipe and drain. My livingroom display is a 56g and the basement sump is a 30g XH that is about 2/3s filled. I never worry about the sump overflowing since there is lots of room in the sump, plus the basement is concrete with a drain next to the sump. What I worry about is a clog in the standpipe/drain or a freak loss of siphon in the U-tube of the overflow. However that being said, I have been running this basement sump for about 10 years without an incident. I have the flow going through the U-tube perfectly matched with the drain capacity so there is not any bubble build up in the U-tube. When I go away on vacation I actually remove the standpipe so the water running through the overflow goes straight down the drain lessening the chance of macroalgae causing a clog. It's loud but nobody is home to hear it anyway. So yes, I think about an overflow but I don't overly stress on it. Should it happen, probably about 10 gallons of saltwater would end up on the livingroom carpet which is not ideal but it's not the end of the world either. It's definitely less catastrophic than a seam breaking and there is always that risk too.