The way to get rid of the, for example, democratic party is by electing DIFFERENT people as democrats - the democratic party will still exist, but the party can change and represent something different than it does now. It's happened before - the current democratic party is different than it was in 1960. The entire South was represented by democrats - now little of it is.
Thom Hartmann is a liberal but he's always taking calls from people unsatisfied with the current democratic party. What he asks them is what they are DOING to change the party - beyond bitching about it. He suggests they join their local party, start recruiting candidates for local office, who then rise to state offices, then national.