i am moving from Magento 1.x to 2.x - I have a lot of custom build extensions from which my business is dependent on - without them I can not work...

So, obviously when we are going to migrate to 2.x, these extensions will stop functioning properly...  

Is there any possibility to fix these extensions with little recode? Or they must be totally rewritten to work ?

Is there any 3rd party support that would make these extensions work on new Magento version?

Please, help. Thanks.