May we replace or add team members if someone drops off the team?

If your team has not started discussing a solution for the Central (long term) Challenge then yes, you may replace lost members. If you have already begun to discuss your solution to the Central Challenge you may not replace the team member(s) who dropped. These dropped team members must remain on your roster. If you had less than seven at the time, then you may add members until your total with the dropped members equals seven.