Yes, all four stories are self-contained and end at good places. There's an unresolved political plotline in the last short story, but not in a cliffhanger way. In addition, developments in "War Games" predicted the events of that story, and you can extrapolate where it's going without feeling like you've been left hanging; the short story's emotional resolution offers sufficient closure.

Oh, and! As one of the other posters notes below, I like others missed the TOS part of your request. The "Reboot" series by seperis responds to STXI (and was written before XII came out, so doesn't address anything in XII).