It absolutely would undermine democracy. A second vote is the only option.
Would it though? Perhaps clearly explaining that the referendum was in fact, advisory, and not a binding vote would go a long way, because it's something that is often ignored and rarely mentioned by the media when discussing Brexit, and doesn't appear to be common knowledge.
The fact that we had an advisory referendum, won by a narrow majority, following a campaign fraught with with illegal funding and outright lies, and that near three years on, we have no clear direction or course of action to actually carry out the result, would suggest to me that there is certainly at least some merit to revoking Article 50.
They could even caveat it with a promise to revisit the result in x number of years, after carrying out proper impact assessments, and detailing actual exit strategies that ensure the country is better off outside of the EU, as should be the case for us to leave.
This "leave at all costs" mentality is absolutely insane, and no government should be pandering so obviously to a group of vocal morons who want something to happen despite the seemingly obvious wide-spread, damaging consequences it will have.
EDIT: Also, any undermining of the democratic process that could have happened has already happened when a) Vote Leave was won through illegal funding and blatant lies, b) a snap election was called to consolidate power for the current PM, but actually only kept her in a job courtesy of a £1 billion bribe slung at a bunch of mercenary, god-bothering lunatics from Northern Ireland and c) the current PM is attempting to table a deal that has already been voted down heavily on two occasions already, without making any changes.