If anyone asked me if pokemon could die, I'd say YES without hesitation. In every generation of the games, there had been cemeteries for pokemons, and there had been NPCs saying how much they were sad after losing their pokemon friends.
Fossil pokemons are obviously "back from the dead" when we revive them, so yeah...
In the anime, Tracey's Scyther was old - so this means that pokemon CAN die from illness/old age/whatever reasons.
But what about Ghost-type pokemons? Can they die? Have they lived for millions of years back when Fossil pokemons were alive?
And how the heck can they even breed? They're made of spirit stuffs... no?