As far I understand bittrex policy they don`t delist tokens/coins that have active development. I think that I read that they don`t delist token/coin if they are only listed on bittrex (meaning it`s listed only on one exchange, I think that I read that on twitter, but can`t be sure).
https://support.bittrex.com/hc/en-us/articles/360000474232-Bittrex-Market-Token-Removal-PolicyIf you see the list that bittrex uses to determinate if they are going to delist token, Coval only stands for Limited trading volume (and not every day) so I think we are pretty safe with bittrex & Coval.