Satoshi, the checkpoint is not used to make a judgement of which chain is better, but just to make sure that very old coins will not be invalidated in the "open" part of the network.

The software could just declare that there is a checkpoint 1000 blocks back. This is an individual checkpoint for each node, and the checkpoints would move forward every time a new block arrives. The checkpoint could never move backwards.

If a longer chain, predating the checkpoint arrived, the node would reject it. This would effectively fork the currency, but so what. In practice, it would just exclude the hidden
part. The "honest" part would continue along. Too bad for those with a long hidden chain. But they chose to be offline for too long.


The network, I see, is one of a lot of online nodes, visible to anyone who wants to see them. This is the core of the network. They will communicate so often, that no one will get 1000 blocks ahead of others. They will transmit their results continously, not collect them in a batch of 1000 blocks.

Then there are potential offline nodes, dishonest nodes etc. If they suddenly show up with a very long chain, there is no reason not to reject them. Or I don't see that reason.

The public internet will never get fragmented, in a major way,for days. And bitcoin is not suitable for such a situation, even though you technically can make it so by erasing all blocks in all but one of the fragmented components after the rejoin. 

You have a manual checkpoint, you say, which exactly shows that checkpoints are possible.