Let's start with the easy part. A clot in the leg can be life threatening. The clot can break off and lodge in the lungs. This is a pulmonary embolism. I had one. They are common and 30% of people who have one die. I was put on bed rest the second they knew I had clots just in case I had some in my legs that would further clog my lungs.
The typical treatment for a leg clot - also known as a DVT or deep vein thrombosis is to use graduated support stockings and take an anticoagulant such as lovenox, heparin, or warfarin. This will prevent new clots and allow the body to do what it can to dissolve the current clot. If warfarin is used, heparin will be given for the 1st week of warfarin treatment to prevent side effects.
New research is showing that using a clot buster type medication locally administered to the venous clots prevents long term leg problems and damage to the vein. While study outcomes have been great, not many places are using this treatment.
Some people with frequent clots will have a filter placed in the leg to catch any clots that may travel to the lungs.
If you have repeated clots, it is recommended that you find a hematologist for additional blood testing. You will want to discover if you have a blood clotting disorder (thrombophilia). This may require specific monitoring and treatment to prevent additional clots.
I have written a number of hubs surrounding clots and am a clot survivor. Feel free to send me a note if you have additional questions. Also, check out http://hubpages.com/health/BloodClotQnA as it will have more information for you.