once the package has been given to the post office, the seller is no longer in control. i think the only shipping rate USPS gives a time guarantee for is express/overnight shipping, priority can take a varied number of days to arrive before it's considered lost. if there was no DOA guarantee by the seller, yeah, there's nothing you can do :/
if they arrive and most/all of them are dead, you could still contact the seller on the odd chance s/he's a merciful person
if they arrive and most/all of them are dead, you could still contact the seller on the odd chance s/he's a merciful person