If Corbyn was elected and gained respect as leader of the opposition the Lib Dems would probably have to take on those of his policies that have support in the centre (see article linked above). By 2020 a lot of Lib Dem supporters will have forgotten about the coalition but the party will know not to risk it again. It may be the best way of getting the Tories out and also have a socialist party with some integrity, even if only getting a share of power through a coalition.

I am probably wrong but would like to hear why.