The very-new 2.0.3.12 Duplicati.CommandLine.exe help advanced seems to think it’s still available, and shows the limitations mentioned in the 2.0.3.10 release notice cited earlier. I can’t say I’ve tried it though.
Before letting this loose, you might consider having B2 snapshot your files, or add some other protection. Possibly the good news in safety is that it used to be automatic, so probably harmless but not too helpful.
The AFFECTED command can show what sort of impact letting dblock files simply stay missing can cause, and right below it, the --list-broken-files and --purge-broken-files may help. Disaster Recovery shows use.
This should only affect the future backups (unlike CrashPlan and perhaps some other backup programs). There are quite a few forum posts from people who are told about extra steps needed to get fast deletion.
Possibly your backups are still healthy enough to start down the Restore path to look at what’s available? Retention (smart or not) should only delete complete backup versions. I don’t think they would cut folders.