When NHL play resumed later that season, Sundin made an immediate impact, leading the Leafs in scoring at a point-per-game pace with 47 points.

Bolstered by the acquisitions of forward Steve Thomas and goaltender Curtis Joseph in the previous off-season, the Leafs made it to the Conference Finals against the seventh-seeded Buffalo Sabres, but were defeated in five games.

When NHL play resumed for 2005–06, Sundin was sidelined in the first game of the season when he was struck in the face with a puck, narrowly missing his eye, but breaking his orbital bone.

In the second game of the season, on 4 October 2007, against the Ottawa Senators, Sundin scored his 389th goal with the club, tying Darryl Sittler's team record.

[16] In Toronto's fifth game of the season, on 11 October, versus the New York Islanders, Sundin scored his 917th point as a Maple Leaf, breaking Sittler's franchise all-time record.

However, one day before the trade deadline he stated that he would not waive his no-trade clause, claiming that he did not believe in being a "rental player" and that if he won the Stanley Cup, he wanted to do it over the course of an entire season.

[21] On the day of free agency, newly appointed Vancouver Canucks General Manager Mike Gillis offered Sundin a lucrative two-year, $20 million contract which, if signed, would have made him the highest paid player in the NHL.

Attempting to entice him to sign with the Canucks, numerous Vancouver businesses extended Swedish-centred special offers, such as a Volvo and IKEA products.

[22] The New York Rangers, Canadiens and Leafs also made contract offers; however, Sundin chose to hold out for the beginning of the season, contemplating retirement.

The return to the Air Canada Centre became highly emotional when a video tribute was paid to the Leafs' franchise leader during a break in the first period followed by a standing ovation.

[33][34][35] On 12 November 2012, Sundin was inducted into the Hockey Hall of Fame alongside Joe Sakic, Adam Oates and Pavel Bure.

[36] In November 2013, Sundin was named as an inductee into the IIHF Hall of Fame, alongside Peter Forsberg, Danielle Goyette, Paul Henderson, Teppo Numminen.

[37] On 10 September 2015, it was announced that Mats Sundin would be added to "Legends Row", a statue outside the Air Canada Centre consisting of 12 of the best players in the franchise's history.

[38] On 15 October 2016, Sundin's number 13 jersey was officially retired by the Toronto Maple Leafs in a ceremony prior to their centenary season home opening game against Boston.

[39] Sundin represented Sweden at various international competitions, including the World Cup and the Winter Olympics, and held the position of team captain for the national squad for the nearly ten years.

[40] Sundin was the captain of the Swedish national team in the 2006 Winter Olympics, leading them to a gold medal with a 3–2 victory over Finland in the final.

[41] In May 2006, Sundin put his four-bedroom house up for sale for a price of $6.499 million, which led to a flurry of media speculation that he was unhappy with the Leafs and sought to move (and play) somewhere else.

On 30 April 2008, Sundin was receiving a leadership award at Our Lady of Lourdes Catholic High School in Guelph, Ontario, when he announced that he and his girlfriend Josephine Johansson were engaged to be married.

[47] Sundin was also a Goodwill Ambassador for the Adopt-A-Minefield Campaign; an organization that raises awareness and funds to end the human and economic suffering caused by anti-personnel landmines.

[48] Sundin was a partner in a Standardbred harness racing horse named Rotation, which in 2003 won the prestigious Maple Leaf Trot at Mohawk Racetrack.