I am losing sales, sure... but TNet was literally selling 2 copies a month prior to me making it deprecated. Hardly worth worrying about.
TNet major downside was always lack of solid documentation. It's currently a more powerful tool than NGUI even, but it will take quite a few brand-new tutorials to show off what it can do and how. I would have been able to do Windward without NGUI quite easily, but I would not have been able to do Windward without TNet at all. TNet handles not only networking in that game but also all serialization for saving / loading, player inventory, game configuration, modding support, etc. It's not something people expect in a networking package, which is why I decided to deprecate the old package until I have time to release a proper update. In its current state TNet is a powerful Unity Extension rather than a networking tool.
I'm still not yet ready to release it -- I just added 100% offline mode to TNet 3 last night for example (doesn't use sockets). This gives all the benefit of serialization / persistent state logic without having to host an actual server. Currently TNet Pro users have access to the github repository and can see and use all the changes, and regular Asset Store license holders can request preview updates by emailing me with their OR#. The PayPal link still works, although like the rest of it the info needs to be updated.