As far as I know, we have no intention to 'shut down' coh on our end. Activity and lifespan will likely rely on the players.
Imagine AoE2 with (much) improved graphics. Would be awesome shit tbh. Never played AoE1 much, sadly. My dad wasn't too pleased when I started playing AoE2 with 9 years, already.
On topic, I don't think it will die instantly, as people will always keep playing the game for a while. However, the competitive scene of CoH1 will probably completly move on to CoH2.