Hi Lynn,
answering your question Re: "Would they go any further in the journey" - this will depend on how you set up journey and segment, imho.
Consent is managed on 2 levels:
1) minimal consent level can be set up for a CJ
2) there are consent related attributes for a contact record - eg "consent given" as well as "allow email"/"allow bulk email". Custom attributes eg "allow text message"can be added - as Clofly has written above. They are used for filtering data in segments and/or creating suppression segments.
With that, in the CJ example you've provided, if your suppression segment will contain all users who opted out either from emails or sms - then this user will not go further with email if he has opted out from sms already (as well as with any other tile as he will be removed from the segment at the moment of first opt-out).
Using CJ minimal consent level will not help much in such case as email and sms sending will probably fall into same category - eg subscriptions/marketing.
Having this in mind, I would recommend
1) either split your CJ into 2 swimlanes within one journey- dividing email and sms sending and setting up different rules/filters
2) or split your CJ into 2 journeys.
#2 is usually recommended unless you will need to have a view of CJs and have combined insights.
HTH
BR
Elena