It always looked likely to be costly - and so it is set to prove.
The 19-13 defeat at Castres in Heineken Cup round one was hard for Saints to stomach.
Barring an early interception try, they were able to keep the French side at arm’s length throughout, dominating possession and territory.
But they couldn’t make it pay, with Dylan Hartley’s opportunistic second-half score the only time they managed to cross the whitewash.
As the Stade Pierre Antoine big band played out in the background and the beer turned flat, the Saints skipper admitted his regret.
It was there for the taking, and Hartley and Co knew it.
So the sight of the French side rocking up at Franklin’s Gardens on Friday night is sure to stir a few emotions.
Because Saints progressing to the Heineken Cup last eight now seems as unlikely as England winning the World Cup in Brazil this summer.
Had they won in France in October, it would be a totally different story.
Saints now need to beat Castres and hope Saracens or Leinster slip up in their games against Connacht and Ospreys, who both have nothing but pride to play for.
So the importance of Friday night’s game at the Gardens can be called into question.
But it does adopt significance for ensuring there are no more regrets.
It is about maintaining the momentum gained from five successive wins in all competitions.
And it is also a chance to book a place in the Amlin Challenge Cup.
That tournament is not the one Northampton wanted to be in come April, because their aims, and rightly so, are far loftier these days.
Mallinder, who has been at Saints since 2007, wants that piece of major silverware to put his team up there with Europe’s elite.
And, should they somehow stay in the Heineken Cup, there is every chance they can spring a surprise in pursuit of the trophy.
But, first and foremost, they will worry about exacting revenge on Top 14 champions Castres, a team they have become all too familiar with in recent seasons.
This is the fourth in succession that the two clubs have battled it out in the pool stages.
And, on the only occasion they won the away game against Castres - the 2010/11 campaign - Saints reached the final.
On the other two occasions they failed to make it out of the pool, and the curse looks set to strike again this season.
But Saints can’t afford to look back in anger.
They will use the experiences gained in this season’s competition to drive them on.
The huge 40-7 Leinster home defeat in December was a seminal experience.
And the win in Dublin a week later showed them exactly what they are capable of.
Now they need to banish the Castres question mark ahead of a big few months in the Aviva Premiership, LV= Cup and, probably, the Amlin Challenge Cup.
And you can bet Saints won’t leave any what ifs on the pitch this time round.