Question for those who know the FA comp rules;
I keep seeing Lee referred to as a rental and I agree the chance of him signing to stay in Cincy would have to be pretty slim but wouldn't he be a type A FA and therefore net the Reds a 1st round and supplemental pick?
If so and we are really just talking about cycling through a couple of prospects (if he could be had for that) then a few months of Cliff Lee, a possible NL Central pennant and even a 1/100th of a chance at keeping him would seem like a no brainer to me. Worst thing that happens is (theoretically) you turn two near MLB ready prospects into two first round draft picks again and had half a season of Cliff Lee in your rotation for the effort.
I know a lot depends on the exact prospects and the situation with Alonzo isn't ideal but if Alonzo and anyone else not named Chapman would do the trick (and my assumption of the comp picks for losing Lee is correct), then I think you do that deal before anyone in Seattle could change their mind.