Trello – What is the Purple Chevron on Trello Cards

They will be unassigned from cards, and that's about it. Their actions will be preserved, as will the fact that they performed the actions.

The Trello guide is a little bit out of date. If you are the owner of a board, you can rename it like so:

1. Click the board title (or the "Board Menu" button)
2. Click "Profile"
3. Click the name of the board (at the top)
4. Type in the new name
5. Click Save