Question moving from Magento 1.x to 2.x – what to do with extensions

i ammoving from Magento 1.x to 2.x – i have alot of custom build extensions from which my buisness is dependent – without them i cannot work…

so obviusly when we are going to migrate to 2.x this extensions will stop to function…

is there any posibility to fix this extensions with little recoding ? ore they must be totaly rewriten to work ?

is there a 3rd party support that would make this extensions work on new magento ?

please help