Please provide an error handling in the flow.
Erros/success output of the action.
So it is possible to react on failed actions.
You can read about this new feature here: https://flow.microsoft.com/en-us/blog/error-handling/
If a failure returns from the HTTP Service (anything other than Success, e.g. 404 etc) then the Flow fails and doesn't continue. It would be better if it was to continue and then conditions based on the Status Code can be added to determine the next action.
Structured exception handling is indeed much needed.
It is currently next to impossible to check if a file exists in certain services (e.g. DropBox) as you get a 404 error (does not exist) when the file does not exist, stopping the Flow.
There are many other examples. As a result we (the team that implemented the Muhimbi PDF Service for Flow) have implemented a switch in each Action to ignore errors so the real status of each Action can be checked after it has completed. This is a kind of 'poor men's error handling', but it works. Details can be found under 'Error handling' in our Core Concepts Knowledge Base article
The way Flow deals with errors appears to be inconsistent as well. Errors that happen inside a For Each do not stop the entire Flow, only that single iteration. This could probably be abused to create some kind of error handler, but it is not pretty.
This is currently possible with Azure Logic apps. We are investigating if we can bring this capability to Microsoft Flow as well.