I would like to see another option for the "When transfer fails" configuration for the data sources. If a source "validation" fails. It could be a simple pre-step that would do a SELECT TOP 1 query for all the fields that would validate if a) a connection can be made and b) that all selected fields are still available in the source. If it fails you could continue with existing data EVEN if tables are in simple mode (truncate after the validation).
Continue with existing data if "validation" fails