Traditionally in Australia, political parties were invisible in the electoral process. Suppose you were voting for 5 senators for your state. All you see on the ballot paper is the names of individuals. The voter numbers the squares, and the magic of single-transferable-vote means that you get proportional representation. So maybe the winning party gets 3 senators and the rival party gets 2. But as far as the electoral process was concerned it was just electing 5 individuals.
This beautiful system was difficult for the voters, so the rules were changed. Now political parties are registered and their names appear beside the individuals, or at the top of a list of individuals. I think this is the way it is in other countries. The problem is that it is no longer clear whether we are voting for people or parties. What should happen when an elected member of parliament decides to leave the party which they had claimed to represent? What if the member was expelled from the party?
The answer is that the voters have to be given some reasonable level of control. This can't extend to reconsulting the voters, which is almost impossible for multi-member electorates. Nor may it depend on the political parties having any rational behaviour or even continuing existence. I have a plan.
The idea is that the ballot paper will show a mixture of individuals and parties. Voters can vote for one or the other or in some systems (such as STV) a combination. More detail on this below. The important thing is: what happens when a party wins, rather than an individual.
When a party registers as a candidate for an election it would provide a list of individuals who will be the custodians of that seat should the party win it. There should also be an individual nominated who will be the person to initially hold the seat.
Now suppose the party wins the seat and their representative is installed. At a later time the nominated custodians can send replacement votes to an appropriate electoral authority. If, during the first half of any month, more than half of the nominated custodians request that the elected representative be replaced with some specific willing person, then that nominee will become the new holder of that seat starting from the beginning of the following month. Additionally 2/3 of the custodians can vote to replace some other custodian in the list.
A nice thing about this is that, for seats held by parties there is no need to make any special arrangements should the sitting member become unable or unwilling to continue.
This can work with any electoral system. For multi-member STV electorates, the political party candidate will only appear once on the ballot paper. It can translate into multiple winners if, after preference distribution, it collects multiple quotas. Also parties can endorse individuals to stand in the same election as well, to gather the votes of those who want a known individual who can't be replaced. However this would be problematic in first past the post systems because it would split the vote.