True, but my model of CO2 is that its damage is proportional to the area under the curve (quanity CO2 * time in atmosphere). So deferring that C02 release by 10 years is strictly a win, b/c you haven't incurred the climate effects of that C02 for those 10 years.

Mostly into the ground, no? Isn't that how petroleum was formed in the first place?

It depends entirely on where the skateboards and other wood-derived waste ends up. If it's not properly disposed of (e.g. litter), then it will release most/all of it into the atmosphere. If it's incinerated, it's all released. If it's in a landfill, it depends on whether and how effectively the landfill is sealed.

Probably not. Most of the oil we find comes from a period when very few organisms could break down waste from dead trees and plants.