There's are a couple of tricks to get round these problems.
- Put your dataflow inside a FOREACH container, with the enumerator is set to 'File' and the 'Enumerator Config' pointing to the file you wish to process.
The dataflow will execute only if that file is found. If not, the package completes (successfully) without doing anything inside the container.
- To prevent the validation error, set the Connection Manager's 'Delay Validation' property to True.