1.
Press Ctrl-Z
This gets you back to the bash prompt.
These days if you press Ctrl-D once it will say there are stopped jobs.
If you press it enough times, the shell will exit and vi will die with it.
2. For older Linux's
Press Ctrl-Z
This gets you back to the bash prompt.
Type:
jobs -l
to see a list of background tasks:
[1]+ 104872 Stopped vi
Then make a note o that number 104872 and type:
kill -9 104872
This will kill vi and not allow it to weasle out of your grip.