Senate majority?
 

This is not really a political question as much as someone who may know more about how the Legislative branch works.

The Senate is held by a slim majority by Democrats. I understand that means the heads of the various committees are Democrats.

But with Teddy Kennedy and Robert Byrd being ill, that majority has shifted.

Or not? I guess both still hold their seats until the unmentionable happens?

Is the seat then appointed by the governor of the state?

Just curious...

They still retain their positions and will be replaced only if they step down or die. If he doesn't stepped down, his staff will do much of the work as they do anyway (the staff can't vote though, but the senator can send in a vote) and democrats retain majority anyway. If he dies or steps down there will be a new election and the regular people decide that is when the democrats could lose majority.