I do not know if using Splenda, for even half of the amount of sugar, in fudge will work. Sucralose (Splenda) just doesn't cook up like normal sugar. I don't think Sucralose, when cooked by itself, will go through the stages of candy that regular sugar does. I tried looking for some recipes, but all I found out there were ads to buy cookbooks for Splenda.
I am a firm believer in the policy of "everything in moderation". I make fudge following the old TNT recipes. But, I don't eat it much. When I was single, I would make a batch that would yield about a pound, and give some of it away to neighbors, or take most of it in to work, and only keeping a little for myself. If I couldn't give it away, I'd wrap it up well and freeze some of it for later.
Peace, Love, and Vegetable Rights!
Eat Meat and Save the Plants!