Whatever roadworks are happening, the contractors usually ( citation needed ) provide access to pedestrians.
Those cyclists prepared to get off and push along the pedestrian access ( citation needed ) can do so.
With planned works this is usually the case. So on encountering a "Road closed $annoyingdistance ahead" I'll usually risk it, as the chances of actually having to backtrack are quite small, and there's a lot to like about getting to ride on miles of access-only road.
I can think of two occasions when there really wasn't any pedestrian access, but some bored looking men in hi-vis let me wheel the bike through their site anyway (on one occasion moving a crane so I could get past). I expect some combination of being female, on an interesting bike in loaded touring mode probably helped, though. At least one occasion where the site was deserted, and I was able to get through by moving a barrier. And one where I actually had to backtrack, because the alternative was scrambling along half a kilometre of steep overgrown verge, or subjecting the bike to steaming fresh tar.
On the other hand, there's a difference between standard resurfacing or diggy hole road closures, and emergency closures due to flooding or bridge failure. That has a much greater chance of being an actual dead end, or at least something you don't want to have to wade through partway through a winter audax. In this case I'd assume the worst and try to route around them.
