magento2 – Question going from Magento 1.x to 2.x: what to do with the extensions

I move from Magento 1.x to 2.x, I have many custom build extensions that my business depends on; Without them I can't work …

obviously, when we are going to migrate to 2.x, these extensions will stop working …

Is there any possibility to fix these extensions with little recoding? Or should they be completely rewritten to work?

Is there a third-party support that makes these extensions work in the new Magento?

please help