As a team member or scrum master do nothing except informing product owner about the situation. Your team already made a commitment to some amount of user stories based on some expected capacity. Something bad happened and one of your team members cannot continue in sprint due to health condition. That can happen and nobody can blame him or you for that.
It is up to product owner to decide what to do next. It is obvious that you will most likely not deliver what you committed. Product owner can let the sprint continue as is so that you complete as many user stories as you can without missing team member and unreasonable overtime or she can decide to stop the sprint and start a new one - but it would be quite drastic.
Descoping is dangerous. Sprint should be a safe zone for the team. It is part of agile principles to empower people. Team is empowered to make a commitment. Once you allow commitment changing during sprint it can soon become a common practice and the whole point of commitment and safe zone will disappear. You will get chaos with continuously changing sprint target.