Get action is enabled in History view and it is possible to get the previous version.
The contents of local file is overwritten silently by previous revision contents, the file gets blue marker as modified.
Now you can modify this file and check it in.
No warnings etc are shown.
However, in usual ST clients the file gets outOfDate status after the previous revision check out. You get the warning on attempt to edit such file and after you invoke check in, you get the Merge dialog to merge your changes with the last revision