Well the short answer is, time will tell.
So much has been written over the past 200 years or so about this most-famous of battles mostly by people far smarter and more learned than me. Waterloo has become synonymous with personal defeat but that's not quite the analogy I am looking for. Indeed the odds and the polls still favour a Conservative / May win. However if May does end up losing her majority (if current polling trends are real and continue) there is an interesting parallel that I think is meaningful.
There is one key aspect to the allied victory at Waterloo that I am alluding to here: Napoleon was fully engaged and withdrawing to fight another day was not an option.
On 18th June 1815 Wellington Offered battle at the Mont-Saint-Jean escarpment, expecting the Prussian Army of Blucher to come to join the fight. As with all such things this is controversial but much has been discussed about how the Prussians were late to the battle such that the English-led army was outnumbered and very nearly defeated by Napoleon's army. However when Blucher's army arrived, the French were broken and fully committed such that they could not withdraw and Napoleon was finally defeated.
It is argued by many that if Blucher's forces had arrived before Napoleon had fully committed his forces, then he would have withdrawn and waited another chance to fight the allies. He only fully committed because he believed the English-led army of Wellington would be fully routed. And they would have been if the Prussians had not arrived when they did. Wellington is recorded as saying "night or the Prussians must come."
The history of the battle and the politics that led to all this - why the Prussians arrived when they did is fascinating and well worth reading about. Of course, this is not the only interpretation of events but it does fit with the facts as far as I know. It is always potentially facile to compare anything to war-fighting - especially when the very experienced soldier, Wellington wished to never see another battlefield after the carnage of Waterloo - the battle he is remembered for (although not his greatest achievement in his own view). However, as I alluded to above, it's not uncommon to use war metaphors for all sorts of things and the concept of one's Waterloo is quite common - there's even an Abba song about it.
Anyway, my point is this, Napoleon was finally defeated because he was fully engaged because he believed he was finally going to defeat Wellington's forces that had pushed him out of Portugal and Spain.
It seems to me, that Mrs May decided to go to the country because Labour could be annihilated and she has gone 'all-in' - to switch to a poker metaphor for a moment. If it wasn't for this belief that she could win decisively then surely she would not have called the election now.
But Labour has had a much better election campaign than the Conservative party and defeating the Conservative party (in the sense of there being no overall majority at least) has become a possibility.
When Theresa May is returned with a majority next week, this will all turn out to be idle wondering but, but, if anything else happens then clearly it will be that choice to fully engage that will prove to be Mrs May's undoing. And surely if it were not for the appearance that Labour were going to be heavily defeated, she would never have countenanced starting this battle in the first place.
So, yes, it could indeed be Mrs May's Waterloo. Indeed if she does not secure a majority, then it surely will be and like Napoleon she must step down from power within a few days of the result.