It seems that Monero will not be able to fix the vulnerability in time.
I noticed today they added checkpoints in preparation for the attack:
https://github.com/monero-project/bitmoneroSo.. what does this mean? Will the checkpoints sufficiently defend against the attack?
The purpose of checkpoints in all cases is to ensure that an earlier part of the chain can't be replaced.
Any new part of the chain would not be affected by checkpoints at all.