The best way is the method described in the Chris White "Yeast" book. Make a small-ish starter like 500ml, throw the suspected dead yeast in the wort and let sit at room temp for a few days. any live, active yeast cells will go into suspension. Pour the liquid only off of the 500ml starter. Put this into the fridge and see how much settles out. Then make a new starter according to how many cells you have. Maybe go with a 250ml as the first step then prop up to 2L for next step etc... by 10x each.
This is the best way to cast aside the dead cells and truly start with viable cells. If you just chuck the old packet into wort then pitch that into your brew you are just transporting dead yeast cells around!