I had not gone thru the experience yet however I would imagine that if the team is not adequately prepared as Hiren stated, then that could be difficult to overcome. The timeline will get pushed back if there is a reasonable justification as to why the schedule needs to be pushed back. If the deadline is critical to the business then the deadline will remain as is. Action items will also always get pushed around or split amongst each team member which is bound to happen. What would be best is to prepare for such events early on in order to circumvent any issues that may arise later which could be detrimental to the completion of the project.