Wouldn't you have the same problem with changing workspaces? Sounds like you can't keep track of anything not currently present on the screen, which before the overview was a lot harder to deal with. One thing that could help is to create a "temporary terminal" keybinding to launch in floating mode so you'll never forget to close it. Or create a focus-or-launch bind that switches to an existing terminal (tools like Nirius can help minimize scripting). The other thing that may help is adjusting your struts so you can see that windows exist to the left or the right. More of general workflow tip than one related to just terminals.