From my understtanding, they just lose their effectiveness... but they arent that expensive, so it may be good to just replace it... or mix it with a fresh batch. there are some "quick shot" type products out there, but I dont know of a pill either... I think that for protein to be efffective it needs to have some quantity to it, and I dont think that you can cram enough into a pill...
as a side note, the best Ive ever used/tasted is the cytogainer.. made by the same company that makes muscle milk... but that stuff is too rich tasting for me... and doesnt have enough protein to use as a main supplement, maybe as an addtional filler though.