How to find lost terminal sessions

I use Terminal for web development, and typically have various tabs open, some of which are divided into multiple session (via tmux).

After a while, I'll accidentally hit command-W and kill one of the tabs ... or do I? When this happens, and a development server was running in the "killed" session, it continues running. I can't see the logs, and I don't know of a good way to kill it, but I can still hit the relevant URL.

This is a bit inconvenient, as I don't always know a good way to find and kill the hidden processes -- ps -ef | grep is not always a nice way to do things. (Particularly with ember-cli, but I'd like to focus on the general question.)

Is there a way to bring back tabs that have been "killed" in this way?