If an Agent moves from one Team to another, will historical data in Analytics maintain based on where they were in the time period you are viewing?

No, Analytics goes with the current team of agent. Data does not get saved for old team of the agent. If you remove agent from a team, data related to that agent will also get removed. 

In this case, best practice will be to download all data for that agent from analytics before moving him to another team. This way you can save all data for that agent.