rsync --recursive --ignore-existing: what (if any) additional flags are needed to resume/repair/overwrite any partially copied files?

Assume an rsync --recursive --ignore-existing foo bar copy command was being run for a large directory tree named foo, but that that command got prematurely interrupted. For example, because of a sudden power failure on the target machine. Running the above command again can save a lot of time for any files/dirs already *fully* copied to the destination bar. But what about any file(s) that was right in the middle of being copied? Presumably, that file exists at the destination in an incomplete/broken state? Having it simply ignored as a "file that's already done" would be very undesirable, of course. Does rsync handle this (extremely run of the mill) scenario intelligently without being directed to do so? (If so, how?) Or does it only do so if specifically instructed by means of more or different flags? Frustratingly, neither the man page nor any vaguely related questions or answers on this site seem to address this very important detail in a clear way. (Sorry if I just didn't look very well.)