Ted has a lot of power. So does it evaporate if he is totally incapacitated (My guess that will be his condition if he even survives) or will it be bestowed on another kennedy. I can’t see Joe have that much power.
But I can see Caroline Kennedy campaigning as the substitute for Ted.
Most of Kennedy’s influence, ability to raise money, etc. has to do with his position in the Senate. If he is incapacitated for the ‘08 election, which he will be if this is a significant stroke, that all halts. Also, his power among DemocRATs in the Senate is amplified because the RATs control the place.