The idea that Jeffords is retiring due to health problems is hot garbage, of course. The real reason why he is retiring is because his political career is DOA. The night he made that backdoor deal with Tom Daschle to give him a chairman seat in that committee was the night he committed political suicide. Facing opposition from both Democrats and Republicans during reelection, being the most impotent member of the Senate, and not to have the support and cash flow that would arise from a political committee doomed Jeffords to a fate that was obvious to anyone. "Retiring" would at least allow him to save face.
Jeffords switching parties hurt the Republicans at first, but it ended up being the best thing that could have happened to them. Jeffords fell on his own knife after threatening to do so for so long, and thus the Republicans could move on with one less nuisance within their own party. Although Jeffords wasn't ran out of the party like he claimed, the Republicans recaptured the Senate with a stronger majority than ever and are better off without him.
If Senator Frist and the rest of the Republican leadership had backbone, they would place even more pressure on the RINO group. After all; they need the Republicans more than than the Republicans need them. If they want to follow the path that Jeffords took, then go right ahead. The only one that is possibly untouchable is John McCain, who won reelection easily last year. The Democrats would be happy to see a couple of them announce they are "independents", and then would try to snatch their seats during reelection.
I have no problems with these senators voting against the party line. The problem is doing so without basing it on principle or to improve your politicial (and popular) standing. If the Republican Party is truly a conservative party, and is willing to follow a conservative agenda, then they'd give these senators an ultimatum: show us your vote, or we'll show you the door.
But the Republicans will never do that because they are more interested in political success rather than conviction. What's ironic, however, is the fact that it will be the obstruction of these senators - and the apathy of the Republican leadership towards them - that will cause the Republican Party to lose the Senate. They can't get anything done due to the fence riders.