"The case with another Scottish referendum is quite different. They could wait to see the outcome and then judge whether leaving the UK would be in Scotland's interests. Personally I think it would be reasonable for the SNP to seek an explicit mandate for an independence referendum in the 2021 Scottish Parliament elections."

I have no doubt that the SNP are hoping that if they go independent early enough then they will be treated as a special case by either being let back into the EU easily/quickly or by not having to leave in the first place.