What about inconsistencies with data outside the database? Things like credit card transactions or other external API calls that were recorded on the master but not the slave will be inconsistent with your slaves view of the world. Is there a standard way of dealing with those kind of things or is that usually handled manually?
You use the logs from the slave to commit the 2nd portion of a two-phase commit, and immediately stop processing new transactions when you only have the slave up.
Your hypothetical API does support two-phase commit correct? Because if it doesn't you have lots of solutions for losing data/creating inconsistent data anyway.
