I've never heard of a 10K race being shut down, because the ones I've done are all part of longer races going on at the same time. If you're truly concerned, the advice to look up last year's times is solid. I'd say they'd be foolish to close the finish line any sooner than 90 minutes, which is still a 15min pace.
Look at the results from last year, see when the last person came in.
Thanks! Don't know why I didn't think of that! Last person was 2 hours. I'm definitely better than 15 minute miles LOL but I just hate being in the last 10%. There's actually not all that many people coming in after 90 min.
Remember... Dead last is better than "did not finish" which is infinitely better than "did not start"!!