Deleting local files is relatively easy via Python (e.g. os.remove(os.path.expanduser('~/Documents/myfile.txt')), but deleting Dropbox files isn't really possible, at least not without pretty significant effort (using the Dropbox API).
Btw, if you want to delete a local file that is currently open, you should open a different file first; otherwise, the editor would automatically save a new file.
Yes, I've seen this too, it seems to be related to iOS 7, it never happened on iOS 6 afaik, but it's not always reproducible, so it's kind of difficult to fix, though I have some ideas for workarounds.
Also, FWIW, I was running iOS 6 (NO jailbreak) on an iPad Mini when I saw the crashes. The only way to get around it was to kill editorial and restart it (it would still be in the multitasking list after the crash), but even that wasn't 100% reliable.