You must add an option to nc. The option depends on the version of nc you are running. For instance, in my case (Kubuntu), the option is -k. From the man page,
-k Forces nc to stay listening for another connection after its current connection is completed. It is
an error to use this option without the -l option.
I cannot promise -k works (unless you are n Ubuntu, of course), you will have to search for something similar. For instance, on my Debian, -k does not exist, but you find:
-q seconds after EOF on stdin, wait the specified number of seconds and then quit. If seconds is negative, wait forever
To check that it works, on one pc:
nc -k -l 0.0.0.0 10000 > out.txt
On a second pc:
echo Hello | nc IP_address_of_first_pc 10000
Issue the command above a few times, then interrupt the nc command on pc1, check number of lines in out.txt.