NEWTs and OWLs aren't necessarily requirements to work or survive in the future. Having them just proves you are certified and capable of doing x type of magic at a certain level like any other job in the real world, however experience is always key.
In addition to the <PERSON> and <PERSON> comment above (leaving and starting up their own joke shop), think of <PERSON> and <PERSON> (who forewent going to Hogwarts for their NEWT year)
"<PERSON> and <PERSON> utterly revolutionized the Auror Department," <PERSON> said. "They are now the experts. It doesn't matter how old they are or what else they've done." - Interview with <PERSON>The Triwizard tournament is also a HUGE deal in the wizarding world. The Champions aren't chosen at random, there is a magic about them being chosen, being worthy enough (not to mention a thousand galleons, that could be invested in the future if they win). The challenges they have to go through are simply extraordinary for wizards, normal older qualified wizards wouldn't stand a chance without preparation. That's got to be worth a NEWT or two...right?
"Why should 'e complain?" burst out <PERSON>, stamping her foot. "E 'as ze chance to compete, 'asn't 'e? We 'ave all been 'oping to be chosen for weeks and weeks! Ze honor for our schools! A thousand Galleons in prize money ­ zis is a chance many would die for!" -GoF
Being a Champion also meant that you were gifted in one way or another (or at least seen in that way by other wizards), gifted enough that those credentials that you were a champion would be with you forever and hold some weight in the eyes of other wizards.
Using the most recent Triwizard champions as examples, at least for <PERSON>, people started treating him like <PERSON>, who was already internationally famous. Note he was already a good student already too.
"Diggory," said <PERSON>. 194
"He must be entering the tournament."
"That idiot, Hogwarts champion?" said <PERSON> as they pushed their way through the chattering crowd toward the staircase.
"He's not an idiot. You just don't like him because he beat <PERSON> at Quidditch," said <PERSON>. "I've heard he's a really good student ­ and he's a prefect." - GoF
and
<PERSON> actually saw the same sixth­year girls who had been so keen to get <PERSON>'s autograph begging <PERSON> to sign their school bags one lunchtime. -GoF
<PERSON> herself was not dim, she was intelligent and gifted, proven by the fact she got a job at Gringotts not 2 years later, backed up by <PERSON> who knew she was intelligent. Gringotts, being the only wizarding bank, would also be extremely hard to get into. Just look at the real world and see how hard it is to work in a bank!
"<PERSON>'s not stupid, she was good enough to enter the Triwizard Tournament," said <PERSON>. - HBP
and <PERSON> was an International Quidditch player, one of the best in the world. His life should be set, especially being just 18 years old.
What about <PERSON>? Well, he's only the main character, the only person to have survived the killing curse...twice, taken down the darkest of all dark lords, and capable of a corporeal patronus at the age of 13.
Also, who would you hire? The 17 year old graduate who has a OUTSTANDING in Defence Against the Dark Arts, or the kid who just took down the don of all evil wizards?
Being seen as a champion put them on a different level to normal wizards. These credentials alone would have been able to get them a job and decent opportunities in their future careers if they didn't have any already. 194