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What is the best way to handle that? Withdraw it? and if yes, how?
Yes, withdrawal is your best and only option. The answer to "how?" is in the text you've quoted (4th paragraph).
No idea what the minimum withdrawable amount is (I don't use Bittrex anymore), but I don't think it's OK for them to still require minimum withdrawal amount for delisted coins, especially when you can't even sell them. They should only be charging network fees.
If you can't withdraw due to your balance being less than the minimum required, you could deposit the missing amount and then withdraw (assuming depositing is still allowed).