Not sure this is something to celebrate. We need a viable government system and that includes opposition either via one or many parties.
Giving carte blanche to one party regardless of their political angle is a recipe for disaster.
Tory voter base changing doesn't give one parry an automatic majority.
The Conservatives just have to adapt their policies for the newer demographics. Instead if giving tax breaks to the rich and punishing everyone else with austerity perhaps if they had policies that people actually appreciated they would gain a larger voter base in the future. The choice doesn't have to be between right-wing (new labour) and far right-wing (Dis-May) parties. As Corbyn has shown there is large support for more centralist ideas. Perhaps in the Future we could could have a centralist Labour and a moderate right-wing Tory party, or even center left labour and moderate right Tories.
the same thing is happening in the US. Republican voters are mostly old white men with strong christian association , low education in rural locations. That is a dying demographic. More women than ever are voting in the US. More people than ever are getting better education and degrees Rural populations continue to decline as there just aren't the jobs in farming and forestry. Moreover, liberals from the coasts are moving to places like Texas and Georgia, changing the reddest of red states into something close to a swing state.
Times change. History has shown that societies do indeed progress, as much as the knuckle dragging neanderthals refuse to accept. Liberals won the the fight to end slavery, give women equal rights, end apartheid, end discrimination based on gender and sexuality, give equal rights to marriage, etc. Over time right wing parties will always have to become more progressive if they want to exist. And in he future, more socialist economic models will be absolutely required to support the growing population with dwindling jobs.