I just hope they will reenable the support.
What I absolutely not understand is, that really old games using the same engine (e.g. No One Lives Forever) are still running via Gamespy, so they have at least one damn old machine for old games running. Couldn't be much of a problem to re-enable TRON support for them and I doubt it will be cost-intensive.
In the meantime, I got a whacky solution for you: I hacked together a simple form to add a server to my existing serverlist on hirnschwund.net. You can enter your TRON server there (use gamespy2 as the type) and it will be listed on the main page next to the two servers I am running on my machine.
As soon as your IP changes they will be gone, though...so it's not a real replacement.
http://hirnschwund.net/?s=add" onclick="window.open(this.href);return false;