This wasteland is already partially destroyed, let's add MORE destruction.
1 day: Power goes out, the pokemon such as Mack's zigzagoon (has no nickname) and Arc the arcanine are shocked by the disappearance of their trainers
1 week: The arch implodes, as it is very weak and can only stand with humans around. Pokemon infest what used to be the world of Fallout: California Adventure.
1 month: Bohrium City's iconic sign falls out of the hills because of a landslide, Arc and the zigzagoon along with other pokemon now live in the ruined buildings.
1 year: The Olympic sinks, every pokemon on it drowns. Relatively large chunks of road are starting to become overgrown rapidly.
5 years: The unusually cartoonish buildings in Toontown start crumbling, especially the bendy ones. Minor earthquakes start happening.
25 years: Toontown is a forest, the Pop Century Hotel has imploded, and earthquakes ravaged Bohrium and Petalburg Cities. Things are looking bad for this world.
50 years: The Big One hits, it is an 8.0 which destroyed everything except half of Downtown, the main hero base, K2 and half of California Adventure.
75 years: The zigzagoon dies, after drowning. The remains of downtown are now glassless, rusted skyscrapers which are most likely missing their tops.
100 years: The remains of Downtown and California Adventure are destroyed, the roof of the hero base's house-like section falls in.
150 years: Arc's children and grandchildren live in the forest which used to be the four minecraft skyscrapers, the base's house-like section burns down.
200 years: The underground part of the base is muddy, and not much remains down there. Let's call it destroyed. The pokemon are slowly getting more and more territory.
500 years: There are over a billion pokemon now, and K2 only remains because it is a mountain. Rich forests hide lots of items, such as toys and devices.
1000 years: Not much has changed other then the PokePopulation reaching 2.5 billion.
100000000000 years: K2 finally erodes down, pokemon have gone extinct and are replaced by a species named Elliosmears.