eshell-kill-processes-on-exit

eshell-kill-processes-on-exit is a variable defined in `esh-proc.el'.
Its value is

nil

Documentation:
If non-nil, kill active processes when exiting an Eshell buffer.
Emacs will only kill processes owned by that Eshell buffer.

If nil, ownership of background and foreground processes reverts to
Emacs itself, and will die only if the user exits Emacs, calls
`kill-process', or terminates the processes externally.

If `ask', Emacs prompts the user before killing any processes.

If `every', it prompts once for every process.

If t, it kills all buffer-owned processes without asking.

Processes are first sent SIGHUP, then SIGINT, then SIGQUIT, then
SIGKILL. The variable `eshell-kill-process-wait-time' specifies how
long to delay between signals.

You can customize this variable.