What if a team member drops out during the swim?

What if a team member drops out during the swim, e.g. they get sick and when it's their turn to swim, they can't face it.

a) Does the team get disqualified, i.e. assuming you swim on with the remain 3 team members? Does anyone (i.e. officials) know/care if this happens?

b) Presumably if they feel better enough to swim later in the day, then there's no problem if they have another go? If this is not a problem, then this tells me that the order in which team members swim is largely irrelevant, i.e. not monitored or deemed illegal if the swimming sequence was to vary, for whatever reason?

Thanks. Hopefully I can get an 'official' answer to this