Plate umpire in Brewer's v . Cubs game

[GBFBUmp]

This is new territory for me. While I am an umpire, I am of the football variety and spend most of my time on that forum.

Last night in the Brewers v. Cubs game, the Home Plate umpire left the game in the second inning, on his own power, but later on the radio I heard he had been sent to the hospital. Anyone know of his condition?

This brought up a question my wife and I were debating. It was interesting to see the rotation of the 1st base ump to home plate, but we were surprised there wasn't a sub at the game, and what would happen if another ump happened to be injured and leave the game. What is the minimum number of umpires for MLB game to continue?

Thanks,
Tim