Is it possible to re-assign tasks if a worker cannot perform them any longer?

If you navigate to Workflow details page in Workflow section, there’s ‘Document Status’ tab that provides access to additional features. Please tick checkbox before the document to be re-assigned, and click ‘Reassign’ button.

It will bring up a popup window, where you can select user(s), who will continue working on the document, and add a note to explain the change.