There's a theory about a "critical mass". If a certain % of UKIP members start again within the Populists, then at some point there will be a tipping point where as many as half could defect. 

The effect of this on UKIP would be to leave it without the rank and file, who would become important members of the PP, rather than cannon fodder for UKIP under a leadership that barely represents their views beyond Brexit... The PP would then carry the torch of Populism passed by UKIP and the remnants of UKIP would broker a merger with the Tories.