In art form that is so temporary, we have a tendancy to view aspects of it as permanent.  We think an improv team will last forever, or take classes with only one person... improv is organic. It stops, and starts. 

If you need to take a break, go ahead. If you want to switch teams, go ahead.  If you want to change the style of your team, go ahead. 

The practice and study of improv is as ethereal as the show.  Allow your journey to ebb and flow, like your improv sets.