In 64 days the UK will leave the EU without a transitional deal (Withdrawal Agreement). This will be a catastrophe for Ireland in that legally a physical border must then be built there. This would mean a breach of the Peace Agreement (Good Friday Agreement, GFA), and may well lead to the return of the Troubles (i.e. so-called physical force Republicanism and its Loyalist counterpart) - guns, bombs, killing, murder, kidnapping, mutilation and all the horrors we had before the 90s ceasefires. Such a scenario is imminent if no deal is reached.
It has often occurred that countries have breached earlier agreements. You vote for what gives you an immediate advantage, or what you critically require in the present moment, but you choose to disregard treaty commitments 2 or 3 or 20 years later, if and only if this proves necessary.
At worst, what breaching the backstop would mean in 2 or 4 years would be what we are otherwise going to have in 64 days.
At best, signing up to the WA means that an FTA (Free Trade Agreement) is reached in a few years time, and that this is part of a package of measures which allows the border to remain free for all time, and that circumstances never require the backstop to be implemented.