Abandoning Afghanistan would be a big mistake by US and other western powers as has been happened in the past. The world was unintentionally silent when America, UK and Pakistan were providing assistance to the Afghan resistance in the 1980's to eliminate the Red army's long-term objectives in Afghanistan.
But there was another menace and its unforeseen consequences, rising side by side with the Afghan resistance, to jeopardise world's peace in the face of the Taliban and al Qaeda. The entire situation in helping Afghan resistance creating and playing a significant role in the rise of Mikhail S. Gorbachev was simultaneous with the fall of Communism in the Soviet Union and Eastern Europe.
This was depicted in the impact on world's politics as well as history, which changed the Communist world. The real mistake of the United States and other Western powers was that they virtually abandoned Afghanistan after the Soviet troops left in 1989.
The resulting vacuum of power created the conditions for the Taliban's seizure of power, and then providing sanctuary for al Qaeda. Further, this safe heaven harboured terrorists in various parts of the world and we are facing serious consequences of the uncontrolled policy made by the United States and the Western powers, right after the Soviet Union left Afghanistan.
Similarly, in Pakistan, the dictatorial government could not sustain its political and geographical boundaries by the impact of al Qaeda and Talibanization. Abandoning Afghanistan again would repeat that mistake, and we won't be able to call the disasters that will follow, unforeseen. Will the United States wish to throw the world's peace in the arena of al Qaeda and Taliban?