You can turn off the automatic snapshot deletion I believe if you dont want this
As for PM, I dont think we delete the backup from PM if a snapshot is created and error happens in unquiesce, only on storage (not 100% sure though).
Sorry to not be more helpful but the CMDs is a simple serial approach to integration, it was not designed for the complexity you are trying to solve. We are working on things in future SC which allow more control over workflows and custom abort steps for each task within a workflow but well that isnt in any SC version you can download and use today. I can just say we do understand the limitations of SC 3.x and are working on addressing them in 4.0 and beyond.
Other than scripting and handling logic yourself I am afraid there arent any other options for SC.
NetApp also has another product called WFA (workflow automator) maybe a combination of SC and WFA would solve your needs?