Don't drive it until it's fixed. The bolt you broke is a hollow bolt that routes oil into that pipe to lubricate the cam and rockers.
An EZ Out is worth a try. You might even be able to tap an appropriately sized screwdriver or chisel into the open end of the bolt shaft and get it turning.
When you replace it, get the updated version from the dealer that has threadlocker on it.
And you didn't screw up that bad. On one my e9, the "professional" who rebuilt the head assembled the springs and washers for one rocker arm in the wrong order, causing it to be off-center of the valve. The only solution? Pull the rocker shaft. On my other car, one of the rocker shafts is the wrong one (a front instead of a rear), so none of the three rockers line up correctly on the valves. The only solution? You guessed it.
THOSE are bad screw ups, in particular because they were both committed by people who charge money to work on BMWs...