O.K. I just went through this with my truck. My boot split right where yours did; I had a new axle but no time to replace it so I decided to drive it until I had time. I drove it for almost 2 months in rainy weather and muddy roads, so I expected it to look awful when I got into it. What I found instead was that there was still a ton of grease in the joint and very little dirt and crap had got into it. Well I changed it out and tore apart the old one and inspected it. It has no damage what so ever; I put a new boot on it and kept it as a spare. In all honesty you could probably wrap it with some duct tape and keep it even cleaner until you get around to changing it out.