If you don't care about connection dropping, indeed just set up key authentication and run ssh in a loop as described above, instead of a complicated VPN, which

If you don't care about connection dropping, indeed just set up key authentication and run ssh in a loop as described above, instead of a complicated VPN, which will only really partially mitigate dropping of -forwarded- connections. Secondly, you should be able to set scripts to trigger when a network interface comes up in most linux distros, but how to do it varies, for example /etc/network/ifup.d/ in ubuntu.