No different to getting to a road that's not actually there (done that), no longer allows cars (done that), unrideable sand/gravel (done that), fenced off (done that) and having to re-route around it on the fly. Online mapping is definitely not perfect.
Last year I ran into trouble when I was trying to route on an access road alongside a main through route, which ended up crossing a couple of fields of cabbages. All trying to avoid about 100m of road which was banned to bikes!
Would be mega lolz if they moved a checkpoint in the briefing.
Imagine the meltdowns