Is there a mod that always lets Twig decay?

NoDecay lets you set the decay rate of all building materials. my twigs decay is about 8 minutes.

even if there is wood in the cupboard?

Kobani

even if there is wood in the cupboard?

You stop the storage of wood in the cupboard.

then not only the basic construction but also the wood crumbles. am I right?

look at NoDecay Plugin, read documentation,