Aveira,
The Gemara and Medrash tell us that of course it was intended to be permanent, just as Chizkiyahu was intended to be Mashiach and just as the Divine plan has been for us to be redeemed in every generation. When we aren’t worthy, it’s delayed until the next generation. That is why every generation that isn’t redeemed is considered to have had the Beis Hamikdash destroyed in their time.