The best (although probably unlikely) outcome is a diplomatic solution that precludes (or makes highly unlikely) any further use of chemical weapons and avoids a military strike. (Perhaps even better would be a Russian/United States brokered cease fire and political solution to the Syrian war, but that seems impossible currently).
Although there is only an extremely slim chance for such a solution, I found it interesting that Putin announced today that Russia had suspended deliveries of sophisticated missile sustems to Syria:
Putin confirmed that Russia had delivered some components of sophisticated S-300 missile systems to Syria but revealed for the first time deliveries had now been halted.
"We have delivered separate components but the whole delivery has not been completed and for the moment we have suspended it," Putin said, without specifying the reason for halting the deliveries.
The contract had been vehemently condemned by the West which argued that Moscow was handing Damascus the firepower to hit back at eventual air attacks.
A military source told the state RIA Novosti news agency after the interview was broadcast that the components delivered by Moscow to Damascus were thus far not enough to mount a single complete S-300 missile system and could not be used as a weapon.
Google: Putin demands 'convincing' proof of Syria chemical attack
It's likely too late, but a diplomatic solution would be preferrable to what likely will come. So long as Syria has chemical weapons and has shown willingness to use them for tactical advantage, the people of Syria are at extreme risk. I understand the argument about red lines and sending a message, but diplomacy can send a message also.
It's still not too late. The real goal is to deter further use of chemical weapons (notwithstanding McCain's pipe dreams). Without Russia's support, Assad is in a very difficult place. It's worth trying to find a diplomatic solution.
Military action always should be last resort, if it all.