What a tough question to answer! and I hope that you are asking this from a theortical point of view and not from your personal experience.
If my current partner would leave me I would totally and utterly fall apart. I am actually making a real effort here to imagine this worst case scenario. I know from previous experiences that after a time of despair I would get my bum into gear and I would drag myself out of that hell.
First of all I would get my appearance sorted: hairdresser, new clothes and a lot of exercise. Then I would declutter my house: burning anything that reminds me of him. Then I would look in the mirror and acknowledge everything that is good about me. Then I would ask my family and friends if they think that something is wrong with me and if this was the case I'd work on improving myself.
Finally, would curse a lot, stick a Limp Bizkit CD on and tell the "curse, curse" to go to hell.
Your 'Team Leader'