http://iscoresports.com/

How should I handle roster changes for instance

Team A has player 1-9 this season, but next season Player 1, 2, 3, 4 leave, and they add player 10, 11, 12?

I shouldn't delete them from the roster in team manager right?

I don't want to add the team as an entire new team, so I can benefit from having scouting info from prior games.

You can set them to Inactive in the roster when they leave a team. Then new games created for the team will not include the Inactive players in the lineups of the new games.