I hope Pat doesn't retire because neither one of the names you mentioned can be considered all that serious challengers. Phil Kline has to worry about getting re-elected Attroney General first. He squeaked in in 2002 against a no-name, under-funded Democrat. He doesn't have that luxury this time. Ryun may be popular in the 2nd District but his speaking in tongues at campaign rally's won't play well in Johnson County. His margin of victory in 2004 was less than Moore's, and Moore will probably cruise in 2006.
I'm not hoping that Roberts retires, and I'm not saying Moore is unbeatable. But I've watched the last 7 elections in this county and I'm saying that you underestimate Moore at your peril. A lot of GOP losers have done just that.
Kansans are a heck of a lot more likely to elect a Democrat Governor or AG or to some other state office than to the U.S. Senate. I don't see why Kline having a tough reelection fight for AG means that he wouldn't defeat Moore handily for the Senate. Remember, Kline nearly beat Moore in 2000, and Kansas as a whole is 6% more Republican than the 3rd CD. As for Ryun's religious conservatism "not playing well" in Johnson County, that's as may be, but I haven't seen any Democrat defeat the equally socially conservative Sam Brownback for the Senate.
And if you don't like those two candidates, how about Congressman Jerry Moran? I doubt Moore would even approach 45% against him in a Senate race.