By the time Sonny Bill Williams was accepting a replacement medal for the one he draped round the neck of a pitch-invading teenager and Dan Carter was being hailed as player of the year, even Richard Curtis would have rejected the script as too saccharine.

But a well-deserved All Blacks victory lap that put the seal on a World Cup the game’s international governing body could barely have conceived in its wildest dreams also raised the stakes. Amid a blizzard of stats proclaiming England 2015 the biggest, best and most commercially successful rugby tournament in history lay a challenge for its administrator, World Rugby.

How to maintain the momentum? How to continue to close the gap between the tier one and tier two nations most thrillingly exemplified by Japan’s last-ditch victory over South Africa?

How to use the second act in what has been bracketed as a defining 12 months for the sport (the introduction of sevens at the Rio 2016 Olympics) to enhance the past six weeks? How to grow the game in the US? How to build on modest ground gained in territories like Germany? And how, in a crowded fixture calendar, to balance the demands of the various competing interests in a way that continues to grow the sport for the benefit of all?

They are problems an exhausted but delighted Brett Gosper, World Rugby’s chief executive, was only too happy to wrestle with the morning after the night before at Twickenham, as the distinctive wrapping that had enveloped the stadium for the duration of the tournament was dismantled in mist.

Top of the list, he agreed, was the need to continue to bridge the gap between tier one and tier two. If Japan and Georgia thrilled with their progress, then others faltered. For all that Gosper was keen to point to the fact that the average winning margin between tier one and tier two had narrowed from 36 to 30 points in four years, the riches realised by this World Cup [at least £80m returned from organisers contributing to an overall estimated take of up to £160m) must accelerate that process.

“We’re obviously going to keep working to close those gaps between tier one and tier two to sustain the competitiveness of world rugby. The calendar is really fixed for the next four years – we have increased the number of tier one versus tier two encounters and the tournaments against their peers as well,” said Gosper.

“We will be involved in strength and conditioning, we’ll be involved in coach selection too. We have a say in those coaches, we help them find the right coaches.”

Japan will benefit from playing more often against top-tier opposition. Ways must be found for the Pacific Island nations and European rising powers such as Georgia to do the same. Promotion and relegation from the Six Nations could be one route to do that.

Even in Japan, where 25m tuned in to watch them beat Samoa as they look ahead to hosting the tournament, the departing coach, Eddie Jones, has hinted at underlying issues among the hierarchy when it comes to growing the game. As the rugby family gets bigger, the sport will become more attractive but also more unwieldly. Add the attractive but unpredictable element of the introduction of sevens at the Olympics into the mix and it’s clear difficult balances will have to be struck.

Just under half of the £350m that World Rugby will invest between 2009 and 2016 will go into the emerging nations, which it argues is a more than equitable split given that 10 teams generate 85% of the revenue.

The International Olympic Committee president, Thomas Bach, was one of those watching from the Royal Box on Saturday and the introduction of the sport in Rio will not only open it up to a huge global audience but increase the amount of rugby played in schools and the government funding available.

“The Olympics is creating more opportunities, pushing more money into the sport of sevens through National Olympic Committees, through solidarity programmes, through the money we actually get for turning up to the Olympics. Being in the Olympics means we find our way on to the curriculum across the world in places like Russia, China but also universities in America and so on,” said Gosper.

“We don’t see them as separate. The Rugby World Cup has a great halo effect on our position in Sevens, the Olympics has a terrific halo effect over 15s. It’s rugby, it’s two different versions and they feed off each other.”

It is perhaps no coincidence that global grassroots participation has almost doubled to 7.2m since the Olympics decision was made in 2009, and it will do wonders for the sport’s exposure in those parts of the world where it remains a mystery.

Difficult issues continue to lurk beneath the surface – from doping to the rulebook to concussion – but compared with the chaotic crisis gripping world football’s governing body and the issues that continue to swirl around the International Cricket Council, rugby can approach its future in a position of relative strength.

As the sun sets on a memorable tournament (at least from a non-English point of view), there will be little time for those who run the game to rest on their laurels. Meanwhile the marketing campaign to shift tickets for Japan 2019, which will bring a whole new set of challenges and opportunities, has already begun.