Most people who used to play on EU_4 play less cRPG now (myself included) and a few have stopped playing entirely.
EU_1 is not the only server to which EU_4 players have moved. There is EU_3, EU_2 and DTV.
So it's not like the population would drastically decrease on EU_1 if we got a small battle server with a maximum of 30 players.
Who knows, maybe the overall player amount would increase instead. Atleast I believe so.