In the ACP-300 exam I had a question like this: You have a scrum team, you works together for 6 months, you have been started a new sprint, after during the sprint 2 members changed with different skills. What should you do?
And there are more answers, but I can't remember more.
I tried to find the answer, but there are lot of different answer. I could not identify the right answer.
This is not necessarily the PMI answer, but practically speaking this is what I would do. First, changing two members in a scrum team is a BIG change, plus they have different skills (as stated). More importantly the personality of the team and how they will work together effectively has change with the addition of the 2 new members. My main goal as PM/ Scrum master would be incorporate the new members into the team and help the team find their optimum level of productivity (velocity). This could take a few sprints.
Regarding the current sprint when the two members left the team, the work they committed to is blocked and should be identified that way. If the new members can pick up the work then they will need to re-estimate the work (with the rest of the team) and commit to what they believe they can deliver by the end of the sprint. If this is not an option and the remaining team members cannot pick up and complete the work left by the departing team members before the sprint review then that work will have to go back into the backlog for re-prioritization. And BTW make sure the stakeholders are informed!
In summary, if I had to pick one of the three listed answers, the one I would chose is "Don't stop the sprint but re-estimate with the new members". It should be understood that any story estimating should be done with the whole team. :)