Will the Magento Extensions created for Magento 1.x continue working for Magento 2 as well or will it require some changes to be done to make it compatible with Magento 2?
No, it will not work and it will require a lot of work to port it to Magento 2.
Their is no direct way to convert extension from Magento 1.x to Magento 2.x
If you provide us the extension if if help us to understand the Logic and work flow.
This will reduce 1/4 time or more to develop the extension in Magento 2.x
If you have any issue feel free to contact us on S K Y P E :- cisin.adrian