If you use H2SO4 to remove the die you will end up with the leadframe and carrier island tangled among bond wires and the die. This page deals with techniques on separating those out.
If you only have one or two its probably easiest to just use tweezers and pick the leads off. However, this also has a larger chance of scratching the die (although this tends to be hard).
Most plastic carrier leads are made out of mostly copper with a silver plating (see vendor carrier materials for details). Nitric acid readily dissolves both. Use a 70% solution as RFNA/WFNA will overheat and decompose more than it will dissolve.
Alternatively, hydrogen peroxide and hydrochloric acid eats both although much less effective.