NetSuite Projects – is there a way to notify assignee that a task is ready for completion based on predecessor task being completed?

I do something similar in script in user event script

When my workItemrecord is saved I compare previous and post values of status and then go find related tasks to move to an open or ready status. then you can drop an email if you want.

code snipets below. Not sure if you could also perform in a WorkFlow.

var prevWorkItem = scriptContext.oldRecord;
var newWorkItem = scriptContext.newRecord;

if(didStatusChangeToComplete(newWorkItem,prevWorkItem))
{
notify user or open new task
}

function didStatusChangeToComplete(newWorkItem, prevWorkItem) {

    var status = newWorkItem.getValue({"fieldId" : "<mycustomField>"});
    var prevStatus = '';
    try {
        prevStatus = prevWorkItem.getValue({"fieldId": "<mycustomField>"});
    }catch{}
    log.debug("status",status );
    log.debug("prevStatus",prevStatus );
    /* !! Caution !!
     * Empty fields from the Old record come back as `null`
     * Empty fields from the New record come back as an empty String
     * This means  you cannot simply compare the old and new
     */
    var changed = ((prevStatus || status) && (status !== prevStatus));
    log.debug("changed",changed );
    return (changed && status == 5);

}