The "winner-take-all" nature of our government assures that there will be at most two parties with any considerable influence at any particular time.
There is no mechanism which assures that the Republican Party or the Demoncrat Party will exist indefinitely. My purpose in becoming a Republican was to kill the Demoncrat Party because it is anti-gun. If the Republicans engage in anti-gun behavior, then my mission becomes to kill both parties.
The Republican Party did not exist at the founding of our nation. The need to pursue abolition of slavery was, I believe, the key reason for its creation. If gunowners must join the Libertarians to assure their rights, then I believe they will.
If Bush signs the AWB, I will be a registered Libertarian the next day.