Till now the NIOS students are allowed to sit for NEET, but there are cases going on Supreme Court regarding the credibility of the NIOS student to participate in such examination. As no verdict have came till now you can obviously opt for the NIOS but your arts result will hold no place in it. It will not expire but it would be of no use either.

To know more about the NIOS visit the link below:

https://school.careers360.com/articles/nios

To know more bout the NEET visit the link below:

https://medicine.careers360.com/exams/neet

I hope this answer helps. All the very best for your future endeavors!