It is impossible for the Lib Dems to lose control of any councils on May 2nd because they don't control any of those being contested. In 2009 they lost Devon to the Conservatives, as well as Somerset. They effectively lost Cornwall as well, although there the council was reborn as a unitary authority and so in a pedantic sense was a new entity.
So in a way the Lib Dems can relax. When you're soaked to the skin you don't mind a walk in the rain. If the Lib Dems end up winning a single one of the 37 councils and mayoralties up for election that will be a good result for them. In fact I think it would be a very good result for them. They do already have a minority administration in Northumberland, and more seats than anyone else in Bristol.
Elsewhere I suppose Cornwall is their best bet. They start from a relatively strong position there with 36 councillors. The Conservative minority administration has had some difficulties. But then so had the Lib Dems when they were in charge. Cornwall has lots of independents – and also a few from Mebyon Kernow – often called Cornish nationalists, although they want a devolved assembly rather an independent nation state. This makes predicting local election results in Cornwall a mugs game.
But, with these low expectations, if the Lib Dems end up with overall control of Northumberland or Cornwall or anywhere going to the polls on May 2nd then they will be pretty pleased.
A good result for the Lib Dems would be for them simply to hold their own in terms of numbers of councillors after heavy losses last year and the year before. They could then say they had stopped the slide. The council by-election results, and the full council election results, last year suggest they will slip back – from the 25% national equivalent vote share they got in 2009 to mid teens. The opinion polls and the fall in the number of candidates they are putting up suggest they will slip back even more substantially.
So given that even reasonable expectations for them are so dire what could possibly constitute a bad result? Last time these councils were contested, the Lib Dems had 484 councillors elected. This time, the councils contesting and the boundaries are slightly different. But the Rallings and Thrasher projections from council by-elections imply a loss of 130 seats. If they do much worse – say lose half their seats and/or come in behind UKIP then that really will be a pretty dismal night for them.