The issue with reopening negotiations over the Irish Border part is it also means all 27 countries can again start jockeying for their own amendments, because that's what reopening it means. They can't just reopen the Irish border issue and nothing else, and at the very least Spain and France have extra things they want to push for, hence the trying to patch it via extra political declarations.
Really the debate around the bill was mostly which worst-case scenario you want:
Do we allow for a hypothetical situation in which the Irish Border could be closed to trade goods seeking to pass without inspection + tariffs (as mandated by WTO rules).
Do we allow for a hypothetical situation where the border remains fully open for trade goods, but separates Northern Ireland from the rest of the UK
Do we allow for a hypothetical situation where the border remains fully open for trade goods, and the UK remains in the Customs Union during the negotiations for a wider trade agreement (which we know would take years by virtue of every other trade agreement taking years to negotiate).
The former is unacceptable to the Northern Irish Republicans, the middle is unacceptable to the Northern Irish Unionists, and the latter is unacceptable to the pro-Leave parts of the English Parliament.
Until those 3 factions, all of whom have enough clout to shut down any exit from the EU, can pick an option it'll remain fucked. And getting those 3 to agree on anything is an impossible challenge. No Deal remains a less popular option than Remain to the UK population as a whole as well, unless you declare the opinions of everyone who votes Remain don't matter which ain't how democracy works I'm afraid. If you use the referendum to remove the remain option, all that does is shift those remain voters over to combine with the smaller-but-still-significant pro-Customs Union leave voters to become the largest group at still-less-than-50%-of-the-population).