Yeah, that's not going to happen. This is the best result ever for the Lib Dems purely because people were sick of the Conservative government. That same animosity is not going to be there in five years time.
It depends which way the Tories go. If a) the Tories elect another extremist and if b) the Tory-Reform split nonetheless persists into a second election, FPTP makes all sorts of crazy outcomes possible.
This is essentially what happened in the 1920s that allowed Labour to displant the Liberals in the first place over the course of two elections. Looking from the position of the 1906 Liberal landslide or even coming out of the First World War when the Liberals were still the largest party, the idea of Labour replacing them as a major party would have seemed fanciful. But the Asquith/Lloyd George split led to two Liberal Parties standing against each other in the 1918 and 1922 general elections, and by the time the Liberals reunited in 1923 the damage was done - Labour had snuck through in Liberal seats to become the 2nd party and, given how relentlessly majoritarian our system is, the reunited Liberal Party was unable to reassert themselves.