Usually recoverable, and usually quickly — provided nobody makes it worse in the first ten minutes by trying things at random on the live site.
If the site is down or broken after an update, the most useful thing is to stop changing things. Updating other plugins to see if it helps, deleting files, or reinstalling on top tends to turn a one-hour fix into a restore from backup.
What actually helps: note exactly what was updated and when, and check whether a backup from before it exists. Those two facts determine whether this is a quick reversal or a longer diagnosis, and they are easy to lose if people start experimenting.
The underlying cause is nearly always a conflict rather than the update itself being faulty — a plugin relying on something the new version changed, a theme calling a function that was removed, or two plugins that both worked until one moved.
What we do
Working UK-wide — directly with businesses, and white label behind design and marketing agencies.
Discuss a projectRestore or revert so the site is serving again. Diagnosis happens on a copy, not on the thing your customers are looking at.
A white screen is not the error. Enabling proper logging turns guesswork into a specific file and line.
On a copy, not live. Usually quick once the error is visible, because the error names the culprit.
Holding a plugin on an old version works today and becomes a security problem later. Fixing the conflict is the real answer.
The update tested on staging first, so the same thing does not happen twice in a week.
Staging, backups and a tested update process. This is what the monthly care hour is for.
Not the update. If changes go to production untested, this will happen again regardless of who fixes it this time.
There is usually still a route. It takes longer and the diagnosis matters more, and the backup position is the first thing we check.
Sites broken by updates sometimes stop updating entirely. That trades a visible problem for an invisible one, and the invisible one is a compromise.
A lot of our work is delivered white label or under agreement, so these describe the problem and the approach rather than naming the client.
Those two facts get us most of the way to the cause. If the site is down right now, call rather than email — and try not to change anything else in the meantime.