They will never officially re-release a classic client. Doing so would revert every change they made in reforged, thus would be Blizzard admitting that reforged is a downgraded abomination. There would be no reason to buy or play reforged. Additionally, even if they did release the classic client, the new terms of service that gimp custom games would still apply.
The only way to revert is to do it yourself. You won’t be able to play BNET, but you will be able to use services like gameranger or other communities to play online as well as LAN services like hamachi if you want to play with your friends. If you want help doing this, check out this thread. For those who want to play Classic Warcraft 3