This report at ConservativeHome about local by-elections from last Thursday was encouraging for UKIP:
In Billericay East Ward, the Tories lost 10.5% to UKIP, although the Conservative councillor was elected.
In Newtown Ward, UKIP gained 22.7% but still ran behind Labour and the Tory hopeful.
In Southway Ward, and in Primrose Ward, UKIP gained against Labour, and in Primrose the swing was nearly 30%! Alas no win in either case.
Finally, a strange new party called Health Concern won a seat from UKIP in Stourport-on-Severn Division.
I would suggest that UKIP is here to stay but needs to build stronger coalitions to win those seats.