Realistically Dak will be 34 in 2027, so the team should at least be considering the position then. Despite his clear physical resurgence this year, Dak has not been as healthy as some other QBs who believe they'll play into their 40's. He's not been as bad as Burrow or Romo (36) wrt his health, but he's been nowhere as clean as Brady (45), Moon (44), or Favre (41) were.
He might be closer to Rodgers (42) who was let go by Green Bay at age 39. Dak's contract covers him through age 35. If you look at Rodger's ratings from age 36-39 (36- 95.4, 37-121.5, 38-111.9, 39- 91.1 and 65/65 of regular season games played) the Packers got good production out of that last 3 year contract (though it was expensive).
If Dallas look to be at all competitive ahead of in 2028, I'm sure we'll see a similar kind of new contract. But if Dallas disappoints again in 2027, I could see the Joneses pulling the trigger in 2028.
Good teams draft their next QB ahead of losing their current one, even if it pisses them off.
Despite their track record, the Joneses actually perceive of themselves as being a good management team, so they might do it. But it would be 2028, I think