ALL yeast should be stored at least at fridge temps. Liquid yeast should be only in the fridge. Dry yeast can also go into the freezer (for longer term storage) without any special treatment. IF you want to freeze liquid yeast you need to use an anti-freezing agent (glycerine typically) in the mix in order to prevent cell damage (from the ice crystals).
I would also wait the full 72 hours from pitching before declaring the yeast dead. Depending on the temperatures they were exposed to, there could have been enough left in the packet to get going. You could just be looking at a longer lag phase. When it gets closer to the 72 hour mark, look at the surface of the wort/beer. IF you see tiny bubbles on the surface (you might need to use a flashlight on an angle) then leave it alone (the yeast are working already).
If you're going to be using liquid yeast in the future, learn about proofing the yeast packs and making starters. While any starter is better than no starter, making a properly sized starter (or two/three steps) can allow you to use a single pack and get the cell count you need for a lot of different OG batches. You can also use starters to get more yeast for old packages of yeast. There's actually an entire book devoted to the subject of yeast
. IMO, it belongs in EVERY brewer's library.