The first Independence referendum was agreed by Westminster on the back of 45% of the popular vote in 2011 and a majority in favour at Holyrood, we can trade opinions on what constitutes a mandate (it really comes down to whether you're a Yes or a No) but like I've said elsewhere if Johnson had the balls and nous he'd go for an early second referendum - it's going to happen anyway and prevarication and demographics will work against your cause.
Brexit can't happen twice, the power grab by Westminster would be part of the next debate and if you won that would really defeat the Independence movement for a generation or as @BigDoddyKane says above more likely forever.